For push mode, convert yyparse from a macro to a function, invoke yylex

For push mode, convert yyparse from a macro to a function, invoke yylex
instead of passing a yylexp argument to yypull_parse, and don't
generate yypull_parse or yyparse unless %push-pull-parser is declared.
Discussed starting at
<http://lists.gnu.org/archive/html/bison-patches/2006-12/msg00163.html>.
* data/bison.m4 (b4_pull_if): New.
* data/c.m4 (b4_identification): Define YYPULL similar to YYPUSH.
* data/push.c: Improve M4 quoting a little.
(b4_generate_macro_args, b4_parenthesize): Remove.
(yyparse): If there's a b4_prefix, #define this to b4_prefix[parse]
any time a pull parser is requested.
Don't #define this as a wrapper around yypull_parse.  Instead, when
both push and pull are requested, make it a function that does that
same thing.
(yypull_parse): If there's a b4_prefix, #define this to
b4_prefix[pull_parse] when both push and pull are requested.
Don't define this as a function unless both push and pull are
requested.
Remove the yylexp argument and hard-code yylex invocation instead.
* etc/bench.pl.in (bench_grammar): Use %push-pull-parser instead of
%push-parser.
* src/getargs.c (pull_parser): New global initialized to true.
* getargs.h (pull_parser): extern it.
* src/output.c (prepare): Insert pull_flag muscle.
* src/parse-gram.y (PERCENT_PUSH_PULL_PARSER): New token.
(prologue_declaration): Set both push_parser and pull_parser = true for
%push-pull-parser.  Set push_parser = true and pull_parser = false for
%push-parser.
* src/scan-gram.l: Don't accept %push_parser as an alternative to
%push-parser since there's no backward-compatibility concern here.
Scan %push-pull-parser.
* tests/calc.at (Simple LALR(1) Calculator): Use %push-pull-parser
instead of %push-parser.
* tests/headers.at (export YYLTYPE): Make yylex static, and don't
prototype it in the module that calls yyparse.
* tests/input.at (Torturing the Scanner): Likewise.
* tests/local.at (AT_PUSH_IF): Check for %push-pull-parser as well.