Here is a detail that needs to be taken care of: we should not use notification on non-file buffers, since that is generally useless (consider the Buffer List buffer) and, with `auto-revert-avoid-polling', prevents these buffers from being polled and thus updated at all.

Patch attached. There is a hack for Dired buffers, since watching their directories happens to be just what we want. It would be nice to generalise this condition somehow, but meanwhile this will have to do, unless you can come up with something better.

A patch for global-auto-revert-mode will come shortly.