MSSQL Server: No accounting for max varchar size when creating columns.

The Doctrine_Connection_Mysql and Doctrine_Datadict_Mysql classes utilise a connection property max_varchar_size so if the field length of a string column is specified and exceeds 255 chars a 'text' column type is used instead of a 'varchar' one.

This logic is missing for MSSQL; Doctrine will attempt to create varchar columns even if greater than the max size (8000 chars).

I've attached a patch for MSSQL which mirrors the MySQL functionality, would you consider including it please?

Thanks!