* data/bison.simple (yyparse): Correct error handling to conform to

* data/bison.simple (yyparse): Correct error handling to conform to
POSIX and yacc.  Specifically, after syntax error is discovered,
do not reduce further before shifting the error token.
Clean up the code a bit by removing the labels yyerrdefault,
yyerrhandle, yyerrpop.
* NEWS: Document the above.