BLD: remove warnings for building parser / hashtable extensions
https://travis-ci.org/jreback/pandas/jobs/194236743

see what we can do about some of these warnings, I think *some* are the result of the uint64 hashtable code. this would be after https://github.com/pandas-dev/pandas/pull/15188 (merging shortly)

in parser.pyx
```
cythoning pandas/parser.pyx to pandas/parser.c
building 'pandas.parser' extension
creating build/temp.linux-x86_64-3.5/pandas/src
creating build/temp.linux-x86_64-3.5/pandas/src/parser
gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ipandas/src/klib -Ipandas/src -I/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include -I/home/travis/miniconda3/envs/pandas/include/python3.5m -c pandas/parser.c -o build/temp.linux-x86_64-3.5/pandas/parser.o -Wno-unused-function
In file included from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/ndarraytypes.h:1777:0,
                 from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/ndarrayobject.h:18,
                 from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/arrayobject.h:4,
                 from pandas/parser.c:437:
/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/npy_1_7_deprecated_api.h:15:2: warning: #warning "Using deprecated NumPy API, disable it by " "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
In file included from pandas/parser.c:439:0:
pandas/src/numpy_helper.h: In function ‘transfer_object_column’:
pandas/src/numpy_helper.h:131:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
In file included from pandas/parser.c:441:0:
pandas/src/klib/khash_python.h: In function ‘asint64’:
pandas/src/klib/khash_python.h:17:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser_10TextReader__get_header’:
pandas/parser.c:9109:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:9177:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:9209:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:10249:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:10308:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:10401:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:10437:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__string_box_factorize’:
pandas/parser.c:22294:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__string_box_utf8’:
pandas/parser.c:22743:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__string_box_decode’:
pandas/parser.c:23203:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__categorical_convert’:
pandas/parser.c:23670:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__apply_converter’:
pandas/parser.c:30308:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:30446:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c:30558:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser__fill_structured_column’:
pandas/parser.c:31598:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/parser.c: In function ‘__pyx_f_6pandas_6parser_10TextReader__get_header’:
pandas/parser.c:10283:61: warning: ‘__pyx_v_data_line’ may be used uninitialized in this function [-Wuninitialized]
gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ipandas/src/klib -Ipandas/src -I/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include -I/home/travis/miniconda3/envs/pandas/include/python3.5m -c pandas/src/parser/tokenizer.c -o build/temp.linux-x86_64-3.5/pandas/src/parser/tokenizer.o -Wno-unused-function
pandas/src/parser/tokenizer.c: In function ‘tokenize_bytes’:
pandas/src/parser/tokenizer.c:747:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:762:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:785:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:827:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:854:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:863:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:900:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:948:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1015:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1033:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1043:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1046:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1049:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1060:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1077:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c: In function ‘parser_consume_rows’:
pandas/src/parser/tokenizer.c:1165:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1202:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c: In function ‘parser_trim_buffers’:
pandas/src/parser/tokenizer.c:1229:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1252:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c:1280:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c: In function ‘_tokenize_helper’:
pandas/src/parser/tokenizer.c:1333:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/src/parser/tokenizer.c: In function ‘str_to_uint64’:
pandas/src/parser/tokenizer.c:1991:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ipandas/src/klib -Ipandas/src -I/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include -I/home/travis/miniconda3/envs/pandas/include/python3.5m -c pandas/src/parser/io.c -o build/temp.linux-x86_64-3.5/pandas/src/parser/io.o -Wno-unused-function
pandas/src/parser/io.c: In function ‘buffer_mmap_bytes’:
pandas/src/parser/io.c:218:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
gcc -pthread -shared -L/home/travis/miniconda3/envs/pandas/lib -Wl,-rpath=/home/travis/miniconda3/envs/pandas/lib,--no-as-needed build/temp.linux-x86_64-3.5/pandas/parser.o build/temp.linux-x86_64-3.5/pandas/src/parser/tokenizer.o build/temp.linux-x86_64-3.5/pandas/src/parser/io.o -L/home/travis/miniconda3/envs/pandas/lib -lpython3.5m -o 
```

in hashtable.pyx
```
cythoning pandas/hashtable.pyx to pandas/hashtable.c
building 'pandas.hashtable' extension
gcc -pthread -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -Ipandas/src/klib -Ipandas/src -I/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include -I/home/travis/miniconda3/envs/pandas/include/python3.5m -c pandas/hashtable.c -o build/temp.linux-x86_64-3.5/pandas/hashtable.o -Wno-unused-function
In file included from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/ndarraytypes.h:1777:0,
                 from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/ndarrayobject.h:18,
                 from /home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/arrayobject.h:4,
                 from pandas/hashtable.c:436:
/home/travis/miniconda3/envs/pandas/lib/python3.5/site-packages/numpy/core/include/numpy/npy_1_7_deprecated_api.h:15:2: warning: #warning "Using deprecated NumPy API, disable it by " "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
In file included from pandas/hashtable.c:438:0:
pandas/src/klib/khash_python.h: In function ‘asint64’:
pandas/src/klib/khash_python.h:17:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
In file included from pandas/hashtable.c:439:0:
pandas/src/numpy_helper.h: In function ‘transfer_object_column’:
pandas/src/numpy_helper.h:131:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_f_6pandas_9hashtable_value_count_float64’:
pandas/hashtable.c:22504:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_2duplicated_float64’:
pandas/hashtable.c:23298:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_f_6pandas_9hashtable_value_count_uint64’:
pandas/hashtable.c:23829:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_6duplicated_uint64’:
pandas/hashtable.c:24623:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_f_6pandas_9hashtable_value_count_object’:
pandas/hashtable.c:25180:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_10duplicated_object’:
pandas/hashtable.c:25824:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_f_6pandas_9hashtable_value_count_int64’:
pandas/hashtable.c:26337:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_14duplicated_int64’:
pandas/hashtable.c:27130:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_16mode_int64’:
pandas/hashtable.c:27456:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_18mode_uint64’:
pandas/hashtable.c:27831:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
pandas/hashtable.c: In function ‘__pyx_pf_6pandas_9hashtable_20mode_object’:
pandas/hashtable.c:28199:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
gcc -pthread -shared -L/home/travis/miniconda3/envs/pandas/lib -Wl,-rpath=/home/travis/miniconda3/envs/pandas/lib,--no-as-needed build/temp.linux-x86_64-3.5/pandas/hashtable.o -L/home/travis/miniconda3/envs/pandas/lib -lpython3.5m -o /home/travis/build/jreback/pandas/pandas/hashtable.cpython-35m-x86_64-linux-gnu.so
```