* build-aux/update-b4-copyright: In warnings, report line
numbers rather than character positions.
* cfg.mk (update-copyright-local): Set to update-b4-copyright so
that update-copyright runs it.
* gnulib: Update.
* build-aux/update-b4-copyright: Do not accept 2-digit
UPDATE_COPYRIGHT_YEAR, which was not handled correctly.
Don't accept a `[' in a b4_copyright argument.
Format code more consistently.
Don't assume b4*copyright never occurs.