Add i18n support to the GLR skeleton. Partially fix the C++

Add i18n support to the GLR skeleton.  Partially fix the C++
skeleton; a C++ expert needs to finish this.  Remove debugging
msgids; there's little point to having them translated, since they
can be understood only by someone who can read the
(English-language) source code.

Generate runtime-po/bison-runtime.pot automatically, so that we
don't have to worry about garbage getting in that file.  We'll
make sure after the next official release that old msgids don't
get lost.  See
<http://lists.gnu.org/archive/html/bison-patches/2005-07/msg00119.html>.

* runtime-po/Makefile.in.in, runtime-po/bison-runtime.pot: Remove.
Now auto-generated.
* PACKAGING: Don't claim that Gawk, GCC, Perl use this method yet.
Fix typos in explanations of the runtime file.
* bootstrap: Change gettext keyword from YYI18N to YY_.
Use standard Makefile.in.in in runtime-po, since we'll arrange
for backward-compatible bison-runtime.po files in a different way.
* data/glr.c (YY_): New macro, from yacc.c.
(yyuserAction, yyreportAmbiguity, yyreportSyntaxError, yyparse):
Translate messages intended for users.
(yyreportSyntaxError): Change "virtual memory" to "memory" to match
the wording in the other skeletons.  We don't know that the memory
is virtual.
* data/lalr1.cc (YY_): Renamed from _.  All uses changed.
Use same method that yacc.c uses.
Don't translate debugging messages.
(yy::yyreport_syntax_error): Put in a FIXME for the i18n stuff;
it doesn't work (yet), and requires C++ expertise to fix.
* data/yacc.c (YY_): Renamed from YY18N.  All uses changed.
Move defn to a more logical place, to be consistent with other
skeletons.
Don't translate debugging messages.
Don't assume line numbers fit in unsigned int; use unsigned long fmts.
* doc/bison.texinfo: Mention <libintl.h>.  Change glibc cross reference
to gettext cross reference.  Add indexing terms.  Mention YYENABLE_NLS.
* runtime-po/POTFILES.in: Add data/glr.c, data/lalr1.cc.