bug#13949: 24.3.50; `fill-paragraph' should not always put the buffer as modified

[Eli Zaretskii]

> Date: Thu, 14 Mar 2013 11:27:25 +0100
> From: Andreas Röhler <andreas.roehler@easy-emacs.de>
> 
> AFAIU the changed-flag presently is set by some commands assumed to change
>   the buffer without regard to the result - as shown.

The flag is set by functions that are about to insert, delete, or
replace portions of a buffer.

> Should not be that complicated to copy the buffers contents into a temporary 
> buffer in this case
> and check both buffers afterwards if being equal.
> 
> IMHO it's worth to do that change wrt fill-commands.

IMNSHO, this doesn't make sense.  E.g., what if the buffer is very
large, and there won't be enough memory to have another copy of it?
Even if it is not that large, why move large amounts of data in this
case?

Emacs uses the gap buffer paradigm precisely to avoid this kind of
lossage.  It doesn't make sense to throw that out the window for the
benefit of a minor improvement.