Not every day you see a patch that nukes 27 files!

* .gnulib: Update to latest, for maint.mk improvements
* bootstrap: Resync to gnulib.
* bootstrap.conf (ACLOCAL): Swap the secondary aclocal include
directory, now that bootstrap picks up gnulib/m4 instead of m4.
* Makefile.am (syntax_check_exceptions, EXTRA_DIST): No longer
worry about nuked files.
* cfg.mk (sc_x_sc_dist_check): Delete dead rule.
(VC_LIST_ALWAYS_EXCLUDE_REGEX): Add HACKING.
(exclude_file_name_regexp--sc_*): Inline and simplify contents...
* .x-sc_*: ...from here, then delete the files.