Filter.v1 methods need to be available when using Filter writers

Format classes that define member methods need to be mixed into other
format classes that use their writers. In this case, methods from
Filter.v1 were missing so a test for Format.WPSExecute failed.

lib/OpenLayers/Format/WPSExecute.js

@@ -16,7 +16,8 @@
  * Inherits from:
  *  - <OpenLayers.Format.XML>
  */
-OpenLayers.Format.WPSExecute = OpenLayers.Class(OpenLayers.Format.XML, {
+OpenLayers.Format.WPSExecute = OpenLayers.Class(OpenLayers.Format.XML,
+                                            OpenLayers.Format.Filter.v1_1_0, {
     
     /**
      * Property: namespaces