bug#13949: 24.4.1; `fill-paragraph' should not always put the buffer as modified

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Cc: 13949@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>
> Date: Mon, 28 Mar 2016 18:29:21 +0200
> 
> So I could just commit the changes I've got here (the new `hash-buffer'
> function and the `M-q' changes, along with unit tests and doc fixes),
> and then we can see how this feels and whether there are any gotchas.
> 
> And then ponder the more general issues later.
> 
> Does that sound OK to everybody?

As optional behavior, yes.  (Plus documentation, please.)