r24848: Make tdb_validate() take an open tdb handle instead of a file name.

r24848: Make tdb_validate() take an open tdb handle instead of a file name.
A new wrapper tdb_validate_open() takes a filename an opens and closes
the tdb before and after calling tdb_validate() respectively.

winbindd_validata_cache_nobackup() now dynamically calls one of
the above functions depending on whether the cache tdb has already
been opened or not.

Michael