Replace ifs in SOG.GroupResize() with Math.Min()

Also fiddle a bit with undo.  This is not currently working properly, though to be fair it also didn't appear to work in 0.7.1.1 either (at least for resize).
Will get some more attention soon.

OpenSim/Region/Framework/Scenes/SceneGraph.cs

@@ -569,6 +569,7 @@ namespace OpenSim.Region.Framework.Scenes
             if (primId != UUID.Zero)
             {
                 SceneObjectPart part = m_parentScene.GetSceneObjectPart(primId);
+
                 if (part != null)
                     part.Redo();
             }