varregion: add --displacement parameter to 'load oar'.

Adds displacment to all objects and terrain loaded from the oar.
As an example, if you have a 512x512 region and an old 256x256 oar, doing
  load oar --displacement "<128,128,0>" oarFile.oar
will load the object (and terrain) into the middle of the 512x512 region.
If displacement is not specified, 'load oar' works like it always has.
If you have a 5

OpenSim/Region/Framework/Interfaces/ITerrainModule.cs

@@ -51,6 +51,7 @@ namespace OpenSim.Region.Framework.Interfaces
         /// </param>
         /// <param name="stream"></param>
         void LoadFromStream(string filename, Stream stream);
+        void LoadFromStream(string filename, Vector2 displacement, Stream stream);
         void LoadFromStream(string filename, System.Uri pathToTerrainHeightmap);
         /// <summary>
         /// Save a terrain to a stream.