(YYERROR): Move code from yyerrlab1 to here, so that

(YYERROR): Move code from yyerrlab1 to here, so that
we don't need to worry about yyerrlab1 being reported as an
"unused label" by non-GCC C compilers.  The downside is that if
locations are used then a couple of statements are duplicated each
time YYERROR is invoked, but the upside is that the warnings
should vanish.
(yyerrlab1): Move code to YERROR.
(yyerrlab2): Remove.  Change uses back to yyerrlab1.
This reverts some of the 2002-12-27 change.