From Marcus Holland-Moritz.
* data/yacc.c (yyerrlab): Move the code that destroys the stack
from here....
(yyreturn): to here. That way, destructors are called properly
even if the stack overflows, or the user calls YYACCEPT or
YYABORT. Stack-overflow problem reported by Marcus Holland-Moritz.
(yyoverflowlab): Destroy the lookahead.