Windows: add AFS_OBJECT_REFERENCE_FS_REQ

Add a new object reference category AFS_OBJECT_REFERENCE_FS_REQ which
is used to avoid overloading AFS_OBJECT_REFERENCE_DIRENTRY.

Change-Id: I428940005dd7b4502329d4171b7307282099af44
Reviewed-on: http://gerrit.openafs.org/9668
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>