Prepare to bulk update copyright years.
* build-aux/update-copyright: New file.
* cfg.mk (gnulib-update): Sync it from gnulib.
(update-copyright-exclude-regexp): New varialbe.
(web-manual): Move...
* maint.mk (web-manual): ...here, to match gnulib.
(update-copyright): New target, copied from gnulib's
maint.mk (it would be nice to sync this file...).
(build_aux): New macro.
(VC_LIST, emit_upload_commands): Use it.
* build-aux/texinfo.tex: Resynchronize from upstream.
* lib/autoconf/general.m4 (_AC_COPYRIGHT_YEARS): Reformat to meet
expected pattern.
* lib/autotest/general.m4 (_AT_COPYRIGHT_YEARS): Likewise.
Signed-off-by: Eric Blake <ebb9@byu.net>