Use git-version-gen for version names between releases.

Use git-version-gen for version names between releases.

* .cvsignore (.tarball-version, GNUmakefile, *~): Add.
* .gitignore (/.tarball-version, /GNUmakefile, /*~): Add.
* .prev-version: New.
* .version.in: Remove.
* ChangeLog: Remove the $Id$ previously used for capturing the CVS
revision.
* GNUmakefile: Remove, now copied from Gnulib.
* Makefile.am: Add code suggested by comments in
build-aux/git-version-gen.
(EXTRA_DIST): Remove GNUmakefile, handled by Gnulib.  Add maint.mk,
.prev-version, and .version.
* NEWS (2.3b+): Rename to...
(?.?): ... this because we're dropping the "+" version naming scheme,
but, in general, we still can't be sure of our next release name.
* bootstrap: Add a quick hack to remove from .gitignore the
GNUmakefile entry that gnulib adds.  We already have a /GNUmakefile
entry.  This should really be fixed in gnulib instead.
* bootstrap.conf (gnulib_modules): Add gnumakefile.
* configure.ac (AC_INIT): Set version name by invoking
build-aux/git-version-gen.
(AC_CONFIG_FILES): Remove .version, now generated by
build-aux/git-version-gen.
* maint.mk: New, copied from coreutils.
* doc/.cvsignore (bison.1): Add.
* doc/.gitignore (/bison.1): Add.
* doc/bison.1: Remove, generated.
* src/.cvsignore (revision.c): Remove.
* src/.gitignore (/revision.c): Remove.
* src/Makefile.am (bison_SOURCES): Remove revision.c and revision.h.
(BUILT_SOURCES): Remove revision.c.
(revision.c): Remove.
* src/getargs.c (version): Don't print revision after the VERSION.
* src/revision.h: Remove.