Alternate algorithm for fixing avatar capsule tilt (Mantis #2905)

Eliminate dynamic capsule wobble. Instead introduce a small, fixed
tilt, and allow the tilt to rotate with the avatar while moving; the
tilt always faces away from the direction of avatar movement. The
rotation while moving should eliminate direction-dependent behavior
(e.g. only being able to climb on top of prims from certain directions).

Falling animation is still too frequently invoked.

Ideally the tilt should be completely eliminated, but doing so
currently causes the avatar to fall through the terrain.

OpenSim/Region/Framework/Scenes/ScenePresence.cs

@@ -2269,7 +2269,7 @@ namespace OpenSim.Region.Framework.Scenes
                     {
                         //Record the time we enter this state so we know whether to "land" or not
                         m_animPersistUntil = DateTime.Now.Ticks;
-                        return "FALLDOWN";
+                        return "FALLDOWN"; // this falling animation is invoked too frequently when capsule tilt correction is used - why?
                     }
                 }
             }