ENH: Support high precision converters in to_numeric
### 

```python
import pandas as pd
from pandas.compat import StringIO
data = StringIO("""
a, b
1, 1
1.7976931348623157e+308, 1
""")
pd.read_csv(data, dtype={'a': float, 'b': float}, engine='python')
```
This work!

```python
import pandas as pd
from pandas.compat import StringIO
data = StringIO("""
a, b
1, 1
1.7976931348623157e+308, 1
""")
pd.read_csv(data, dtype={'a': float, 'b': float}, engine='c')
```
This fail!
Message: ValueError: cannot safely convert passed user dtype of float64 for object dtyped data in column 0


### Full error stack:

```
ValueErrorTraceback (most recent call last)
<ipython-input-4-f830b6441439> in <module>()
      5 1.7976931348623157e+308, 1
      6 """)
----> 7 pd.read_csv(data, dtype={'a': float, 'b': float}, engine='c')

/usr/local/lib/python2.7/dist-packages/pandas/io/parsers.pyc in parser_f(filepath_or_buffer, sep, delimiter, header, names, index_col, usecols, squeeze, prefix, mangle_dupe_cols, dtype, engine, converters, true_values, false_values, skipinitialspace, skiprows, nrows, na_values, keep_default_na, na_filter, verbose, skip_blank_lines, parse_dates, infer_datetime_format, keep_date_col, date_parser, dayfirst, iterator, chunksize, compression, thousands, decimal, lineterminator, quotechar, quoting, escapechar, comment, encoding, dialect, tupleize_cols, error_bad_lines, warn_bad_lines, skipfooter, skip_footer, doublequote, delim_whitespace, as_recarray, compact_ints, use_unsigned, low_memory, buffer_lines, memory_map, float_precision)
    707                     skip_blank_lines=skip_blank_lines)
    708 
--> 709         return _read(filepath_or_buffer, kwds)
    710 
    711     parser_f.__name__ = name

/usr/local/lib/python2.7/dist-packages/pandas/io/parsers.pyc in _read(filepath_or_buffer, kwds)
    453 
    454     try:
--> 455         data = parser.read(nrows)
    456     finally:
    457         parser.close()

/usr/local/lib/python2.7/dist-packages/pandas/io/parsers.pyc in read(self, nrows)
   1067                 raise ValueError('skipfooter not supported for iteration')
   1068 
-> 1069         ret = self._engine.read(nrows)
   1070 
   1071         if self.options.get('as_recarray'):

/usr/local/lib/python2.7/dist-packages/pandas/io/parsers.pyc in read(self, nrows)
   1837     def read(self, nrows=None):
   1838         try:
-> 1839             data = self._reader.read(nrows)
   1840         except StopIteration:
   1841             if self._first_chunk:

pandas/_libs/parsers.pyx in pandas._libs.parsers.TextReader.read()

pandas/_libs/parsers.pyx in pandas._libs.parsers.TextReader._read_low_memory()

pandas/_libs/parsers.pyx in pandas._libs.parsers.TextReader._read_rows()

pandas/_libs/parsers.pyx in pandas._libs.parsers.TextReader._convert_column_data()

pandas/_libs/parsers.pyx in pandas._libs.parsers.TextReader._convert_tokens()

ValueError: cannot safely convert passed user dtype of float64 for object dtyped data in column 0

```
<details>
### pd.show_versions():
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-139-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: zh_CN.UTF-8
LOCALE: None.None

pandas: 0.22.0
pytest: None
pip: 9.0.1
setuptools: 38.4.0
Cython: 0.27.3
numpy: 1.14.0
scipy: 1.0.0
pyarrow: None
xarray: None
IPython: 5.5.0
sphinx: 1.6.6
patsy: 0.5.0
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: 3.4.2
numexpr: 2.6.4
feather: None
matplotlib: 2.1.2
openpyxl: None
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: None
lxml: None
bs4: 4.6.0
html5lib: 0.9999999
sqlalchemy: 1.2.2
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: 0.6.0
</details>

