Fixed bug where read_csv ignores dtype arg if input is empty.
The `CParser` implementation for `pd.read_csv` ignores argument `dtype` if the input is empty.  This pull request fixes this so that a DataFrame with the expected column types is returned.

``` Python
import pandas as pd                                                                                           
import cStringIO as stringio                                                                                  

data, dtype = 'a,b', 'i'

df = pd.read_csv(stringio.StringIO(data), dtype={'a': dtype})                                                                                                                                                               
assert df.dtypes[0].kind == dtype, "df.types[0].kind = %r, dtype = %r" % (df.dtypes[0].kind, dtype)
```

``
Traceback (most recent call last):
  File "issue_1.py", line 9, in <module>
    assert df.dtypes[0].kind == dtype, "df.types[0].kind = %r, dtype = %r" % (df.dtypes[0].kind, dtype)
AssertionError: df.types[0].kind = 'O', dtype = 'i'

```
```
