* NEWS: Bison-generated C parsers now use the _ macro to

translate strings.
* data/yacc.c (_) [!defined _]: New macro.
All English strings wrapped inside this macro.
* doc/bison.texinfo (Bison Parser): Document _.
* po/POTFILES.in: Include src/parse-gram.c, since it now
includes translateable strings that parse-gram.y doesn't.