Fix impure push parser compile error reported by Bob Rossi at

Fix impure push parser compile error reported by Bob Rossi at
<http://lists.gnu.org/archive/html/help-bison/2008-02/msg00023.html>.
* data/yacc.c: Clean up whitespace in the output a little.
(yypstate_allocated): Define for impure push parsers regardless of
whether the pull interface is also requested.
* tests/push.at (Push Parsing: Multiple impure instances): Extend to
check impure push parsers without the pull interface.

* data/yacc.c (yypstate_new): Don't try to invoke yyerror since
yyerror takes arguments specified by %parse-param while yypstate_new
does not.
* doc/bison.texinfo (Parser Create Function): Document that
yypstate_new returns 0 for multiple impure parser instances.
* tests/push.at (Push Parsing: Multiple impure instances): Update
expected stderr output.