Windows: AFSVerifyEntry purge file data on DV change

Windows: AFSVerifyEntry purge file data on DV change

If the data version change is detected during AFSVerifyEntry(),
treat it the same as if the AFS_OBJECT_FLAGS_VERIFY_DATA flag
had been previous set.  Purge the old data from the Windows
file cache.  Be sure to set the new metadata after the purge
so that if the file length was truncated the old data beyond
the truncation point will still be purged.

Change-Id: I80c33f303c6499f22955e9874b2f4c50d666a3cb
Reviewed-on: http://gerrit.openafs.org/7048
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>