Added an imageList.clear() to osgbillboard so that its memory would be

cleared before entering the viewer main loop, this removes memorymanager
a reported memory leak due to the viewer using exit() which bypasses
the clean up on main itself.

Added an osgNew to the ReaderWriterRGB.cpp to aid detected of tracking of
memory leaks.

src/osgPlugins/rgb/ReaderWriterRGB.cpp

@@ -338,7 +338,7 @@ class ReaderWriterRGB : public osgDB::ReaderWriter
             RawImageGetData(raw, &data);
             RawImageClose(raw);
 
-            Image* image = new Image();
+            Image* image = osgNew Image();
             image->setFileName(fileName.c_str());
             image->setImage(s,t,r,
                 internalFormat,