Fix bug such that the first pushed token's value and location are

Fix bug such that the first pushed token's value and location are
sometimes overwritten (sometimes by %initial-action) before being used.
* data/push.c (yypush_parse): Rename arguments yynchar, yynlval, and
yynlloc to yypushed_char, yypushed_val, and yypushed_loc for clarity.
For the first yypush_parse invocation, initialize yychar to YYEMPTY to
more closely mimic the pull parser logic.
Don't copy the pushed token to yychar, yylval, and yylloc until it's
time to read a token, which is after any initialization of yylval and
yylloc.
(gottoken): Rename label to...
(yyread_pushed_token): ... for clarity and to avoid infringing on the
user namespace.