Windows: track cm_rootUser connections

Windows: track cm_rootUser connections

Add CM_UCELLFLAG_ROOTUSER flag to cm_ucell_t for the purpose
of tracking which connections belong to the cm_rootUser.

Reviewed-on: http://gerrit.openafs.org/6207
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 2495d02951fa1a9f6f48cc2a5bc7750f310dae75)

Change-Id: Ie0014200d9e3ed3832bf875a9788aad1f55f29ec
Reviewed-on: http://gerrit.openafs.org/6813
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>