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

[Óscar Fuentes]

Andreas Röhler <andreas.roehler@easy-emacs.de> writes:

> Another solution would hash only the paragraph in question, re-format
> it in a temp buffer and replace original content only if changed.

If we know the paragraph's begin and end points, we can hash just that
range and then there is no need of a temporary buffer. I think that this
condition is met on all cases.

Anyway, I've made some experiments and hashing a 160 MB file on a 8 year
old 2.4 GHz 64 bit workstation takes 2.4 seconds.