* bootstrap: Get runtime translations into runtime-po.

* bootstrap: Get runtime translations into runtime-po.
Create runtime-po files automatically, if possible.
* configure.ac: Invoke BISON_I18N, so that we eat our own dog food.
* data/yacc.c: Rewrite inclusion of <libintl.h> so that ENABLE_NLS
does not infringe on the user's name space.
(YYENABLE_NLS): Renamed from ENABLE_BISON_NLS.
* doc/bison.texinfo (Internationalization): Revamp the English
and Texinfo syntax a bit, to try to make it clearer.
(Bison Options, Option Cross Key): Mention --print-localedir.
* m4/bison-i18n.m4 (BISON_I18N): Rename ENABLE_BISON_NLS to
YYENABLE_NLS.  Quote a bit more.
* runtime-po/.cvsignore: New file.
* runtime-po/Makefile.in.in (mostlyclean): Remove *.old.pot.
* runtime-po/Rules-quot: Remove; now created by bootstrap.
* runtime-po/quot.sed: Likewise.
* runtime-po/boldquot.sed: Likewise.
* runtime-po/en@quot.header: Likewise.
* runtime-po/en@boldquot.header: Likewise.
* runtime-po/insert-header.sin: Likewise.
* runtime-po/remove-potcdate.sin: Likewise.
* runtime-po/Makevars: Likewise.
* runtime-po/LINGUAS: Likewise.
* runtime-po/de.po: Likewise; we will rely on the translation project
to maintain this, so "bootstrap" should get it.
* src/getarg.s (PRINT_LOCALEDIR_OPTION): Let the C compiler determine
its value.
* src/main.c (main): Bind the bison-runtime domain, too.

* data/yacc.c: Include <libintl.h> when NLS is enabled.
(YYI18N): Renamed from _. Use dgettext when NLS is enabled.
* po/POTFILES.in: Remove autogenerated file src/parse-gram.c.
* runtime-po: New directory.
* runtime-po/Makefile.in.in: New file, copied from po/, with modified
$(DOMAIN).pot-update rule, so that old messages are never dropped.
* runtime-po/Rules-quot: New file, copied from po/.
* runtime-po/quot.sed: Likewise.
* runtime-po/boldquot.sed: Likewise.
* runtime-po/en@quot.header: Likewise.
* runtime-po/en@boldquot.header: Likewise.
* runtime-po/insert-header.sin: Likewise.
* runtime-po/remove-potcdate.sin: Likewise.
* runtime-po/Makevars: New file.
* runtime-po/POTFILES.in: New file.
* runtime-po/LINGUAS: New file.
* runtime-po/bison-runtime.pot: New file.
* runtime-po/de.po: New file.
* m4/bison.m4: New file.
* Makefile.am (SUBDIRS): Add runtime-po.
(aclocaldir, aclocal_DATA): New variables.
* configure.ac: Add AC_CONFIG_FILES of runtime-po/Makefile.in.
Define aclocaldir.
* src/getargs.c (usage): Document --print-localedir option.
(PRINT_LOCALEDIR_OPTION): New enum item.
(long_options): Add --print-localedir option.
(getargs): Handle --print-localedir option.
* doc/bison.texinfo (Bison Parser): Remove paragraph about _().
(Internationalization): New section.