tds 7.2 support and variant support

I just finished merging patches for tds 7.2 (mssql 2005) and variant.
Variant type can now be read by all libraries (even dblib).
tds 7.2 currently works only for odbc (there are problems with blobs
using this version with dblib and ctlib due to missing textptr
informations from server). MARS are still not supported but it's the
first step to support them (they not works with version 7.1).
I also added version "7.1", previously called "8.0" to conform to MS.
Version "8.0" is still available for compatibility. Internally we
still use 8.0 for mssql 2000 and 9.0 for mssql 2005.

Regards
  Frediano Ziglio