WebDAV locking

[thiloplanz]

One day, there should be proper WebDAV locking.

Probably two implementations, one that maintains locks in MongoDB (on the file metadata), and a more lightweight version that keeps track of locks in-memory.

For now, you can set up "fake" locking, which does not do anything, but just pretends that locking is implemented. That seems to be enough to make Mac OS X Finder mount a WebDAV share in read-write-mode (without locking, it will be read-only).

 #locking.provider = fake