Fixes [#1011267] and [#1011085]. Fixes problems with money support.

Negative money support and other bugs were caused by representation format
differences caused by the culture configured for the server. By forcing a
culture agnostic format, we get a consistent behavior. From now on,
Npgsql uses the 'C' locale for monetary.
Added testcase based on bug report "[#1011085] Money format is not set in
accordance with the system locale format"