Make building of Debian revisions work.

Make building of Debian revisions work.

* Makefile (distclean): Don't remove anything in debian/, since it will
  never be necessary.
  (debclean): Removed, since two different targets need slightly
  different versions of this.  Even abstraction has its limits.
  (debbuild): New target that takes care of performing the build itself.
  (debrevision): New target that makes a revision build, where the
  original tarball must not be modified.
  (debrevision): Split out building stuff to debbuild target.

* debian/changelog: Several revisions worth of Debian fun.

* debian/control (Build-Depends-Indep): Add emacs21 | emacsen.
  (Description): Make this match the ITP and shorten the text.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-202