Deal with source dir being deleted and recreated

[mpartel]

When the source dir is deleted, bindfs should watch for it being created again and update its cwd.

Could be implemented as follows:

1. Add an inotify watch on the cwd path.
2. Check that the dir wasn't already deleted.
3. Wait for IN_DELETE_SELF or IN_MOVE_SELF.
4. Periodically poll for the path to reappear, or make an inotify-based system, which takes volatile parent dirs into account (would probably be something like a recursive version of the present algorithm).
5. When the path reappears, fchdir into it.

All this either in a new thread or use the low-level FUSE API and use async I/O with watches and the FUSE fd.

[mpartel]

Could also be implemented as a separate watcher script.