Windows: Avoid deadlock in invalidation path

Windows: Avoid deadlock in invalidation path

During data version invalidation the AFS redirector must CcPurge
any non-dirty extents on a file. This operation can be intercepted
by a filter driver which in turn might open the file and close it
again before the CcPurge completes.

The AFSPerformObjectInvalidate call holds the ExtentsResource
shared which can deadlock if AFSClose attempts an extent tear down
which requires exclusive access to the ExtentsResource.

Change-Id: I7cb0289d8036aabf56bb11fd12a79308be45faa8
Reviewed-on: http://gerrit.openafs.org/6856
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>