Set source masks that include the editsession's allowed regions to ForwardExtentCopies

Fixes #710

worldedit-core/src/main/java/com/boydti/fawe/util/EditSessionBuilder.java

@@ -457,4 +457,8 @@ public class EditSessionBuilder {
         return wnaMode;
     }
 
+    public Region[] getAllowedRegions() {
+        return allowedRegions;
+    }
+
 }