Improve auto-revert-mode support
Improve auto-revert-mode support

* Split out the code dealing with auto-revert-mode into a separate
  section.
* Actually set auto-revert-interval (the previous code did not work).
* Only autorevert buffers that are visible (should improve performance).
* Revert stale buffers without a prompt when using find-file.

raxod502/radian,raxod502/radian