Undo most of the 2002-11-12 yychar -> yytoken patch, as it broke

Undo most of the 2002-11-12 yychar -> yytoken patch, as it broke
GCC 3.2.1 (which depends on yychar == YYEMPTY when there is no
lookahead symbol, and which sets yychar in parser actions) and it
disagreed with the Bison documentation.  This should fix the bug
reported by Andrew Walrond in
<http://mail.gnu.org/pipermail/bug-bison/2002-December/001949.html>.

(YYTRANSLATE): Don't check for negative argument,
as the caller now does that.
(yyclearin, YYBACKUP, yyparse): Use yychar, not yytoken.
(YYEMPTY): Parenthesize right hand side, since others use it.
(yyparse): Don't assume that our generated code is the only code
that sets yychar.