1) driver name comparison for MS SQL Server workaround is realy kinda dirty
   hack, but for now i don't know how to code it more carefully
2) another dirty hack: length of LONGVARCHAR and LONGVARBINARY fields is
   currently set to MAX_ATTR_LEN. Maybe such fields must be handled with
   SQLGetData() instead of SQLBindCol(), but it is said in documentation,
   that it is guaranteed to work only when such column goes after last bound
   column. Or should we get ALL columns with SQLGetData (then something like 
   _SQLFetchAsStrings() wrapper would do SQLGetData() for all columns)...
3) in some cases (particularly, when using OpenLink Generic ODBC driver with
   MS SQL Server), it returns "Function sequence error" after all records are
   fetched. I really don't know what it means, and after all
    - it works with any other driver I tried
4) ldapsearch sometimes refuses to show some attributes ("NOT PRINTABLE" diags)
   on Win32 (on linux everything's fine)
5) back-sql crashes on invalid filters (to be fixed ASAP)
   