Windows: mountpoints always have a trailing dot

Windows: mountpoints always have a trailing dot

when expanding a cell alias to a full cell name the trailing
dot was forgotten when putting the mountpoint string back
together.

Reviewed-on: http://gerrit.openafs.org/5427
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 17be9b775c0be234879eeda66707581e23a18d08)

Change-Id: I2e3fbfb922614d9888e9e6957bff66bbb407abfa
Reviewed-on: http://gerrit.openafs.org/5429
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>