Windows: cm_Rename break in 9cf7a628c2ff178b2fa236d2c0a41ca9be315036

Windows: cm_Rename break in 9cf7a628c2ff178b2fa236d2c0a41ca9be315036

9cf7a628c2ff178b2fa236d2c0a41ca9be315036 broke renaming of
a file to a name that does not exist.  Put back the code that
makes that possible with a comment.

Reviewed-on: http://gerrit.openafs.org/5735
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 7a426424b7fb45659f6000a564e8c71a9108a33c)

Change-Id: Ia82ddc46b303cb80380c342d44db437c490b8508
Reviewed-on: http://gerrit.openafs.org/6043
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>