Add Sourcegear Vault/Fortres ghost folders.

http://download.sourcegear.com/misc/vault/help/client.3.5.1/ghostfoldersandfiles.htm
These are folders created by Sorucegear's versioning system Vault (A.K.A. Fortress) for its tracking purposes. It's the same as ignoring $tf/ for Microsoft's Team Foundation Server, which is right above the lines I added.