Updates to osgprerender to support use of rendering to an image, rather then

just a texture.

src/osgDB/Registry.cpp

@@ -59,6 +59,7 @@ Registry::Registry()
     initFilePathLists();
 
     // register file extension alias.
+    addFileExtensionAlias("sgi", "rgb");
     addFileExtensionAlias("rgba", "rgb");
     addFileExtensionAlias("int",  "rgb");
     addFileExtensionAlias("inta", "rgb");