odbc: connection-string allow any freetds.conf option

[Kokan]

The aim is to be transparent, and allow any freetds.conf configuration option in the ODBC connection-string, so user do not require freetds.conf string.

[fziglio]

The patch seems sensible. Some considerations:

• the options in ODBC are case insensitive, the option in libTDS are case sensitive, I think he easiest fix for this inconsistency would be to have all case insentitive;
• there's no check for function result, I think we should consider valid_configuration field in odbc_parse_connect_string;
• odbc_parse_connect_string fills parsed_params for the supported ODBC parameters but not for libTDS options. This feature is used to fill ConnStrOut in SQLDriverConnect allowing to expand the connection string to a full independent connection string. I think we can ignore this but it would be better if we could support this too.

[Kokan]

Thanks for the feedback. I'll update the PR with your points.