s3-winbind: Add an update function for winbind cache.

s3-winbind: Add an update function for winbind cache.

With 57b3d32 we changed the format for the winbind cache database and
the code deleted the database for the upgrade. As this database holds
also cached credentials, removing it is not an option. We need to update
from version 1 to version 2.

Autobuild-User: Jeremy Allison <jra@samba.org>
Autobuild-Date: Sat Dec  3 03:47:58 CET 2011 on sn-devel-104
(cherry picked from commit a3f600521122d1a6d74d16668bd1ea4447c5c867)

The last 3 patches address bug #8658 (Negative / positive winbind cache won't
expire till opposite type of query is made).