(YYERROR): Now just 'goto yyerrorlab', since the

(YYERROR): Now just 'goto yyerrorlab', since the
macro's size was becoming unwieldy.
(yyerrlab): Do not discard an empty lookahead symbol, as this
might destroy garbage.
(yyerrorlab): New label, with the old contents of YYERROR,
plus the following change: pop the stack of rhs corresponding
to the production that invoked YYERROR.  That is how Yacc
behaves, and POSIX requires this behavior.
(yyerrlab1): Use YYPOPSTACK instead of its definiens.