* Patch from Thomas Schwinge to switch from --svn to --rcs=svn, etc,

* Patch from Thomas Schwinge to switch from --svn to --rcs=svn, etc,
  to pave the way for adding other RCS support. This also changes the
  setup files, where before they had svn => 1 or svn => 0, now they have
  rcs => "svn" or rcs => "".
* Add a debian/NEWS file with upgrade notes.
* Load whatever rcs module is specified, so new ones can be just dropped in
  as plugins and work.
* Add some basic docs about writing RCS modules.