Added keystone file handling

include/osgViewer/Keystone

@@ -68,6 +68,12 @@ public:
     osg::Geode* createKeystoneDistortionMesh();
     
     osg::Node* createGrid();
+    
+    /** Write the file specified by the "filename" user value field. Return true if file successfully written. */
+    bool writeToFile();
+    
+    /** convinience function that loads and assigns any keystone files specified in the DisplaySettings::KeystoneFileNames list, return true if Keystone's assigned to DisplaySettings.*/
+    static bool loadKeystoneFiles(osg::DisplaySettings* ds);
 
 
 protected: