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: ofv@wanadoo.es,  jwiegley@gmail.com,  13949@debbugs.gnu.org
> Date: Sun, 27 Mar 2016 18:11:47 +0200
> 
> What about the text property representation -- can that easily be
> hashed, do you think?

One could hack something together along the lines of
compare_string_intervals and intervals_equal, I think.  That is,
traverse the tree as they do, and compute the hash while at that.