build: Modernize autogen.sh.
* autogen.sh: Update from GnuPG. * autogen.rc (version_parts): New. * configure.ac: Change to use autogen.sh --find-version helper. * Makefile.am (dist-hook): Do not create VERSION (EXTRA_DIST): Add VERSION.
- Signed-off-by: Werner Koch <wk@gnupg.org>