glr: allow spaces between "%?" and "{" in predicates

Reported by Rici Lake.
http://lists.gnu.org/archive/html/bug-bison/2013-10/msg00004.html
http://stackoverflow.com/questions/19330171/

* src/scan-gram.l: Do not try to be too smart when diagnosing invalid
directives.
* tests/glr-regression.at (Predicates): New test.

THANKS

@@ -110,6 +110,7 @@ R Blake                   [email protected]
 Raja R Harinath           [email protected]
 Ralf Wildenhues           [email protected]
 Richard Stallman          [email protected]
+Rici Lake                 [email protected]
 Rob Vermaas               [email protected]
 Robert Anisko             [email protected]
 Rob Conde                 [email protected]