Windows: AFSExamineVolume drop TreeLock if waiters

After each call to AFSExamineObject drop the ObjectInfoTree.TreeLock
if there are threads waiting for access.  The garbage collection process
should not delay real work.

Reviewed-on: http://gerrit.openafs.org/9786
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 5952cc139c102035591e8c95bbba313cf709d332)

Change-Id: I78ef97395e18c4377a56cb3e6ce6a24eda4cdd5c
Reviewed-on: http://gerrit.openafs.org/9823
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>