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

[Drew Adams]

I think it is unwise to _replace_ willy-nilly the longstanding
definition of buffer modification - for either users or Lisp
code.  Just because you think you can do something clever using
hashes, that does not mean that you should, if it changes the
longstanding behavior.  No gratuitous loss, please.

On the other hand, as I said, it might be good to expand that
notion to different _kinds_ of buffer modification - not only
for indication to users, but also for code.

IOW, additional flexibility, why not?  But replacement, no thanks.

I said:

  There are different kinds of buffer changes.  It would be
  good to have ways to detect these as such.

The indication to users could perhaps be to use other chars for
this, in addition to `*', in mode-line indicators `**' and `%*'.

Any such change in the indication should be optional, e.g.,
controlled by a user option.

There are two things that a user might want to customize here:
(1) which kinds of buffer change to indicate and (2) how to
indicate them.

Wrt #2, a user could choose, for example, not to use different
markers for different buffer changes, i.e., to always use only
`*', even if s?he uses #1 to define "change" (only text changes,
text and text-property changes,...) for the given buffer.  (The
option could be buffer-local, of course.)