Remove some unnecessary differences between the pull parser code and

Remove some unnecessary differences between the pull parser code and
the push parser code.  This patch enables yynerrs in push mode.
* data/push.c: Reformat M4 a little.
(b4_yyerror_range): Remove and convert all uses to just yyerror_range.
(b4_declare_scanner_communication_variables): Don't omit yynerrs just
because push mode is on.  Instead, if pure mode is on, move yynerrs
to...
(b4_declare_parser_state_variables): ... here.
(yynerrs, yyerror_range): For push mode, #define each NAME in this list
to yyps->NAME so it can be used in yypush_parse.
(yypush_parse): Don't omit uses of yynerrs in push mode.