that they arn't created on the stack inappropriately.
Split the implemention of Matrix up so that it is a simple no referenced counted
class and can be safefly created on the stack. To support referenced counting a
seperate subclass now exists, this is RefMatrix which inherits from both Matrix and
Object.
PositionAttitudeTransform, removed the equivialnt callbacks once found in these
transform classes.
Changed the NodeCallback class so its derived from osg::Object instead of
osg::Referenced to allow it to be saved out in the .osg format.
Added support for Update and Cull callbacks into the .osg file format.
Added support for AnimationPathCallback into the .osg file format.
