Toggle Global Auto Revert mode.
With a prefix argument ARG, enable Global Auto Revert mode if ARG
is positive, and disable it otherwise. If called from Lisp,
enable the mode if ARG is omitted or nil.
Global Auto Revert mode is a global minor mode that reverts any
buffer associated with a file when the file changes on disk. Use
`auto-revert-mode' to revert a particular buffer.
If `global-auto-revert-non-file-buffers' is non-nil, this mode
may also revert some non-file buffers, as described in the
documentation of that variable. It ignores buffers with modes
matching `global-auto-revert-ignore-modes', and buffers with a
non-nil vale of `global-auto-revert-ignore-buffer'.
This function calls the hook `global-auto-revert-mode-hook'.
It displays the text that `global-auto-revert-mode-text'
specifies in the mode line.
(fn &optional ARG)
Non-nil if Global-Auto-Revert mode is enabled.
See the command `global-auto-revert-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `global-auto-revert-mode'.