Make llGetMass() return total mass of object when called on root prim.

As per http://lslwiki.net/lslwiki/wakka.php?wakka=llGetMass
Aims to resolve http://opensimulator.org/mantis/view.php?id=5954

OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs

@@ -2907,7 +2907,10 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
         public LSL_Float llGetMass()
         {
             m_host.AddScriptLPS(1);
-            return m_host.GetMass();
+            if (m_host.IsRoot)
+                return m_host.ParentGroup.GetMass();
+            else
+                return m_host.GetMass();
         }
 
         public void llCollisionFilter(string name, string id, int accept)