For push mode, add pull wrappers around yypush_parse.

For push mode, add pull wrappers around yypush_parse.
* data/push.c: (b4_generate_macro_args, b4_parenthesize): New macros.
(yypull_parse): New function wrapping yypush_parse.
(yyparse): New #define wrapping yypull_parse.
* tests/calc.at (_AT_DATA_CALC_Y): Call yyparse even when %push-parser
is declared.
* tests/headers.at (export YYLTYPE): Make yylex global.  For push mode,
prototype yylex in the module that calls yyparse, and don't prototype
yyparse there.  Otherwise, the yyparse expansion won't compile.
* tests/input.at (Torturing the Scanner): Likewise.