YYACCEPT, YYERROR, and YYABORT, as user actions, should not

YYACCEPT, YYERROR, and YYABORT, as user actions, should not
destroy the RHS symbols of a rule.
* data/yacc.c (yylen): Initialize to 0.
Keep its value to the number of items to possibly shift.
In particular, a regular successful parse that ends on YYFINAL by
a (internal) YYACCEPT must not have yylen != 0.
(yyerrorlab, yyreturn): Pop the RHS.
Reorder a bit to emphasize the `shifting' bits of code.
(YYPOPSTACK): Now accept a number of items to pop.
* data/lalr1.cc: Likewise.
* data/glr.c: Formatting changes.
Use goto instead of fall through.
* doc/bison.texinfo (Destructor Decl): Complete.