Windows: add cm_HaveToken

cm_HaveToken answers the question of whether a cm_user_t has a
token for a specified cell.

Change-Id: I4dff312a7e9000ccee6952c21fca174700364c4c
Reviewed-on: http://gerrit.openafs.org/9076
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>