ODEPlugin

* Added osSetPrimFloatOnWater(BOOL) to make Physical prim float at the water level.   
* osSetPrimFloatOnWater(TRUE); or osSetPrimFloatOnWater(FALSE);
* By default, prim do not float at the water level.
* More work is needed on the floating, but it's a start.

OpenSim/Region/Physics/BasicPhysicsPlugin/BasicPhysicsPlugin.cs

@@ -254,6 +254,11 @@ namespace OpenSim.Region.Physics.BasicPhysicsPlugin
             set { return; }
         }
 
+        public override bool FloatOnWater
+        {
+            set { return; }
+        }
+
         public override bool IsPhysical
         {
             get { return false; }