GCC compiler warnings
should sort these out prior to release. all look very straightforward

```
python setup.py build_ext --inplace
running build_ext
cythoning pandas/src/tseries.pyx to pandas/src/tseries.c
warning: /home/wmckinney/pandas/pandas/src/moments.pyx:486:53: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/moments.pyx:488:54: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:21:45: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:56:71: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:116:57: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:148:45: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:198:44: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:238:52: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:269:52: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:321:46: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:337:50: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:378:54: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:425:46: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:441:50: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:453:50: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:520:54: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:553:54: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:576:54: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:622:60: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:669:57: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:685:61: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:736:65: local variable 'ret' referenced before assignment
warning: /home/wmckinney/pandas/pandas/src/hashtable.pyx:768:65: local variable 'ret' referenced before assignment
building 'pandas._tseries' extension
gcc -pthread -fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/opt/py27/lib/python2.7/site-packages/numpy/core/include -I/opt/python27/include/python2.7 -c pandas/src/tseries.c -o build/temp.linux-x86_64-2.7/pandas/src/tseries.o
In file included from pandas/src/tseries.c:243:
pandas/src/skiplist.h:61: warning: function declaration isn't a prototype
pandas/src/skiplist.h: In function 'skiplist_insert':
pandas/src/skiplist.h:189: warning: unused variable 'tmp'
In file included from pandas/src/tseries.c:244:
pandas/src/khash.h: At top level:
pandas/src/khash.h:589: warning: function declaration isn't a prototype
pandas/src/khash.h:594: warning: function declaration isn't a prototype
pandas/src/khash.h:603: warning: function declaration isn't a prototype
pandas/src/khash.h:605: warning: function declaration isn't a prototype
pandas/src/khash.h:606: warning: function declaration isn't a prototype
pandas/src/khash.h:607: warning: function declaration isn't a prototype
/opt/py27/lib/python2.7/site-packages/numpy/core/include/numpy/__ufunc_api.h:227: warning: '_import_umath' defined but not used
pandas/src/tseries.c: In function '__pyx_pf_6pandas_8_tseries_14Int64HashTable_4get_iter_test':
pandas/src/tseries.c:69783: warning: '__pyx_v_val' may be used uninitialized in this function
pandas/src/tseries.c: In function '__pyx_pf_6pandas_8_tseries_14Int32HashTable_4get_iter_test':
pandas/src/tseries.c:68338: warning: '__pyx_v_val' may be used uninitialized in this function
```
