Ignore X and Y body rotations when sent by mouse look.

Fixes http://opensimulator.org/mantis/view.php?id=3274
When not in mouselook, avatar only sends rotations around the Z plane (since that's the only way an avatar can rotate).
However, in mouselook it also sends X and Y information.  But sending X and Y in terse updates causes issues with wrong camera movement in mouselook.
So strip out X and Y components for now.  If this is an issue, then could strip out before sending avatar terse update, though this generates more cpu work.
Thanks to mirceakitsune for suggesting an initial fix