Windows: Remove trailing slash on non-root directories

For the FileNameInformation and FilePhysicalNameInformation queries
a trailing slash is required for the \\server\share\ path but is
not required for directories below the root.

Change-Id: Iabbe7daed4f60ad995c04c70dfb2992af095281e
Reviewed-on: http://gerrit.openafs.org/11489
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>