Windows: Create Symlinks in Volume Roots

Permit the CreateSymbolicLink API to create symlinks in volume
root directories.

Change-Id: I779f127f9a7e4ddfee41fe7a9398f20175843be0
Reviewed-on: http://gerrit.openafs.org/9656
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>