Windows: Directory validation should purge data changes immediately

Windows: Directory validation should purge data changes immediately

During AFSEnumerateDirectory() and AFSVerifyDirectoryContent() calls
use AFSPerformObjectInvalidate() instead of AFSInvalidateObject()
to trigger the data purge.  This is necessary to avoid a race as
AFSInvalidateObject() will queue a work request that will be performed
after the metadata is updated.

Change-Id: Iaf09c6448927a037175cb4a83502fd4a1d210ef2
Reviewed-on: http://gerrit.openafs.org/7279
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>