Switch to single intervals for FSF notices,
and consistently put them first.
Update copyright notices for 2024.
* cfg.mk (update-copyright-env): Use UPDATE_COPYRIGHT_FORCE=1,
UPDATE_COPYRIGHT_USE_INTERVALS=2.
* patch.man: Always use \(co, so that update-copyright
updates these dates.
* src/version.c: Correct Larry Wall copyright years.
* configure.ac: Add automake and gnulib macros, replace several
obsolete macros.
* Makefile.am, lib/Makefile.am, src/Makefile.am, tests/Makefile.am:
Add for automake.
* autogen.sh, INSTALL, Makefile.in, mkinstalldirs, update-version.sh:
Obsolete; remove.
* README-hacking: Import from diffutils, replace cvs with git.
* build-aux: Move gnulib auxiliary files here from the top-level
directory.
* gnulib: Add gnulib git submodule.
* bootstrap, bootstrap.conf: Import from gnulib and adjust.
* gl/lib: Remove gnulib files from the repository; they are now
imported into lib/ from gnulib as needed.
* tests/test-lib.sh: Use $abs_top_builddir exported from
tests/Makefile.am here instead of $PWD.
* m4/utimbuf.m4: This macro has been removed from gnulib. Add it here
for now; this will be replaced by gnulib's utimens module soon.
