Fixed crash when deleting last watcher

Ignore-this: 589e1e5907ff289262f809d2f09a80eb

darcs-hash:20091103200534-56b4d-828ff18d7bf3925c18e0770f80d784b2bc9d4dbd
Improved notifications related code

Ignore-this: f6e0a555447c2ba5ffd1ecefef273f57

darcs-hash:20091103132036-1e3d8-0a75f7c158266be28b957a05e328b41dcb635f5a