better cleanup of t/var

better cleanup of t/var

Add an END action in t/lib/dbixcsl_test_dir.pm to delete t/var, first
closing any open DBI handles because if there is an open SQLite handle
to a .db file in that dir, the .db file cannot be removed on Win32. Also
copy the file to t/backcompat/0.04006/lib/dbixcsl_test_dir.pm.

Also add t/var to MANIFEST.SKIP just in case.