Patch from Michael Osias IBM (jimbo2120)

In his own words: 
If a prim becomes a listener or remote channel and the script is deleted, it cannot become a listener or channel again with a new script.  
This patch fixes that.

OpenSim/Region/Environment/Interfaces/IWorldComm.cs

@@ -40,5 +40,6 @@ namespace OpenSim.Region.Environment.Interfaces
         ListenerInfo GetNextMessage();
         void ListenControl(int handle, int active);
         void ListenRemove(int handle);
+        void DeleteListener(LLUUID itemID);
     }
 }