BUG: Conflict between thousands sep and date parser.

I've fixed the C parser portion. The issue there was that it did not handle the case where parse_dates is a dict.

Python parser fix yet to come. That test still fails.

Example:
    s = '06-02-2013;13:00;1-000,215;0,215;0,185;0,205;0,00'
    d = pd.read_csv(StringIO(s), header=None, parse_dates={'Date': [0, 1]}, thousands='-', sep=';', decimal=',')

Then d should have a column 'Date' with value "2013-06-02 13:00:00"

Closes issue https://github.com/pydata/pandas/issues/4678