bug#23276: 25.0.92; Crash in auto-revert when file no longer present

[Anders Lindgren]

And I still am not convinced that deleting a file under auto-revert
shouldn't erase its buffer.  Otherwise, it sounds like just
half-auto-revert to me.  Would we keep the buffer non-empty if the
file existed but was empty?

When I originally wrote auto-revert mode I decided that Emacs should not clear a buffer when the corresponding file was removed, as a safeguard against a file accidentally being removed. Today, I still think that is the correct way to handle this situation.

The current patch handles a special case when the file is removed after it has been decided that it should be reverted, but right before the actual revert -- it should be treated just like a normal file delete.

I think disabling auto-revert mode is not correct way to handle this -- the file might be temporary removed by, say, a version control system and might reappear a moment later, in which case we want it to be reverted into Emacs.

    -- Anders