Support for different queries based on DBMS versions #23

Adapt dbms modules/methods/xml queries file for usage with different versions of the dbms.

For instance, kb.dbmsVersion is already used within MSSQL to determine how to re-enable the xp_cmdshell procedure. This will also be useful for Firebird and in general replaces the ugly "query"/"query2" used in the queries.xml with some proper "minver"/"maxver" that specify which query apply to which dbms version.

To be worked closely to ticket #24.