Change to using CVS, not RCS, to do our revision text extraction.

Change to using CVS, not RCS, to do our revision text extraction.

Resolves issues 4, 11, 14 and 29.

* www/cvs2svn.html: Update dependency from RCS to CVS.
* design-notes.txt: Amend the note on the handling of ,v file newphrases.

* cvs2svn (get_co_pipe): Use a piped "cvs co -p" instance, not a "co" instance.
    Simplify arguments.
  (generate_ignores): Adapt to above.
  (CVSRevision.rcs_path): No longer required. Delete.
  (DumpfileDelegate._add_or_change_path):r
    Adapt to changed get_co_pipe invocation.
  (main): Tweak error message.
    Seek out a CVSROOT directory, to signify we really have been passed a CVS
    repository.
    Test for a working cvs executable, with and without the -R option.

git-svn-id: http://cvs2svn.tigris.org/svn/cvs2svn/trunk@1298 be7e6eca-30d4-0310-a8e5-ac0d63af7087