Various maintainer cleanups.

* .cvsignore: Add a.exe, a.out, b.out,, conf[0-9]*, confdefs*,
conftest*, for benefit of CVS commands run at the same time as
"configure".  Add build-aux, since "bootstrap" now creates it and
its subfiles.
* Makefile.cfg (move_if_change): Remove.
* Makefile.maint: Remove the update stuff; we now use "bootstrap".
(ftp-gnu, www-gnu, move_if_change, local_updates, update):
(po_repo, do-po-update, po-update, wget_files, get-targets):
(config.guess-url_prefix, config.sub-url_prefix):
(ansi2knr.c-url_prefix, texinfo.tex-url_prefix):
(standards.texi-url_prefix, make-stds.texi-url_prefix, taget, url):
($(get-targets), cvs-files, automake_repo, wget-update, cvs-update):
Remove.
* configure.ac (AC_CONFIG_AUX_DIR): Change from config to build-aux;
this is now the recommended name.
* config/.cvsignore: Remove config.guess, config.rpath, config.sub,
depcomp, install-sh, mdate-sh, missing, mkinstalldirs, texinfo.tex,
ylwrap.  These files now go into build-aux.
* config/move-if-change: Remove.
* config/prev-version.txt: Bump from 1.75 to 2.0.