* src/reader.h, src/reader.c (gram_error): ... can't get

* src/reader.h, src/reader.c (gram_error): ... can't get
yycontrol without making too strong assumptions on the parser
itself.
* src/output.c (prepare_tokens): Use the real 0th value of
token_translations instead of `0'.
* src/parse-gram.y (yyerror): Don't rely on yycontrol being
visible here.
* data/yacc.c (yyreport_parse_error): Rename yylocation as yylloc
for the time being: %locations ought to provide it to yyerror.