Windows: Fix symlink and mount point make \\afs\xxx handling

Windows: Fix symlink and mount point make \\afs\xxx handling

When processing a request to make a symlink or a mount point
in the afs root volume (\\AFS) the smb redirector will fail
the request because a server name by itself is not a valid path.
Therefore, we insert the "all" share component to refer to the
root volume as a valid path.  \\AFS\foobar becomes \\AFS\all\foobar.

A recent change stripped the trailing slash from the string
returned by Parent().  This broke the test that determines
whether or not the provided path that failed the IsAFS() test
is in fact referring to the \\AFS server and requires the insertion
of the "all" share name.

This patchset permits the test to work with \\AFS or \\AFS\
and removes extraneous directory separators from the generated
path containing the "all" share.

Change-Id: Idf5f934aaa22c71789ab7970a8e3cd48e1a79d44
Reviewed-on: http://gerrit.openafs.org/3928
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>