Windows: cm_ShutdownSCache corrections

Windows: cm_ShutdownSCache corrections

Obtain cm_scache.dirlock, cm_scache.rw and cm_scacheLock
in the correct order.

Do not release cm_scache.rw when it is not held.

Since the cm_scacheLock is being dropped, preserve the value
of scp->allNextp prior to dropping the lock.

Reviewed-on: http://gerrit.openafs.org/5279
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit c58ae34f72d25434cd59228806ca59a6ff39a903)

Change-Id: I65f3c4be5436031cdd99d912b0277b54d4033bf6
Reviewed-on: http://gerrit.openafs.org/5282
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>