Toggle reverting tail of buffer when the file grows.
With a prefix argument ARG, enable Auto-Revert Tail mode if ARG
is positive, and disable it otherwise. If called from Lisp,
enable the mode if ARG is omitted or nil.
When Auto Revert Tail mode is enabled, the tail of the file is
constantly followed, as with the shell command `tail -f'. This
means that whenever the file grows on disk (presumably because
some background process is appending to it from time to time),
this is reflected in the current buffer.
You can edit the buffer and turn this mode off and on again as
you please. But make sure the background process has stopped
writing before you save the file!
Use `auto-revert-mode' for changes other than appends! (fn &optional ARG)