adds releaseSourceMeshData() method to IMesh and Mesh for freeing mesh data after conversion to pinned lists.

OpenSim/Region/Physics/Manager/IMesher.cs

@@ -47,6 +47,7 @@ namespace OpenSim.Region.Physics.Manager
         int[] getIndexListAsInt();
         int[] getIndexListAsIntLocked();
         float[] getVertexListAsFloatLocked();
+        void releaseSourceMeshData();
         void releasePinned();
     }
 }