Reinstate former extended character class rules.

Reinstate former extended character class rules.

* lisp/muse-regexps.el (muse-regexp-use-character-classes): Looks like
  extended regexps really don't work well on Emacs 21.2 or 21.3, so
  document that.
  (muse-regexp-emacs-revision): New variable that indicates the revision
  number of this version of Emacs.
  (muse-extreg-usable-p): Reinstate old rules -- Emacs 21.2 and 21.3
  aren't working well enough with extended character classes in regexps.

* lisp/muse.el (muse-version): If INSERT option is given, insert the text
  instead of just displaying it.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-212