Changed DisplaySetting::instance() to return a ref_ptr<>& rathern than a raw C pointer to enable apps to delete the singleton or assign their own.

include/osg/DisplaySettings

@@ -15,6 +15,7 @@
 #define OSG_DisplaySettings 1
 
 #include <osg/Referenced>
+#include <osg/ref_ptr>
 
 #include <string>
 #include <vector>
@@ -33,8 +34,7 @@ class OSG_EXPORT DisplaySettings : public osg::Referenced
     public:
 
         /** Maintain a DisplaySettings singleton for objects to query at runtime.*/
-        static DisplaySettings* instance();
-
+        static ref_ptr<DisplaySettings>& instance();
 
         DisplaySettings():
             Referenced(true)