yacc.c: always initialize yylloc

The initial location might be used if the parser starts by an empty
reduction, so really ensure proper initialization of the initial
location.  The previous approach fails for PostgreSQL, which uses
Reported by Peter Eisentraut.
http://lists.gnu.org/archive/html/bug-bison/2012-11/msg00023.html
With help from Théophile Ranquet.

* data/yacc.c (b4_declare_scanner_communication_variables): Be sure
to initialize yylloc, even when its structure is unknown.
(yyparse): Simplify the call to b4_dollar_pushdef.
* tests/actions.at (Initial location): Check of similar pattern
as in the case of PostgreSQL.

THANKS

@@ -88,6 +88,7 @@ Pascal Bart               pascal.bart@epita.fr
 Paul Eggert               eggert@cs.ucla.edu
 Paul Hilfinger            Hilfinger@CS.Berkeley.EDU
 Per Allansson             per@appgate.com
+Peter Eisentraut          peter_e@gmx.net
 Peter Fales               psfales@lucent.com
 Peter Hamorsky            hamo@upjs.sk
 Peter Simons              simons@cryp.to