[vtkusers] UserTransform in vtkCamera

[Eigil Samset]

The current Transform in vtkCamera is computed as:
Transform = UserTransform*PerspectiveTransform*ViewTransform

To me this does not make any sense. For what I would like to do 
(controlling camera position and orientation by an external transform), 
this would make more sense:

Transform = PerspectiveTransform*UserTransform*ViewTransform

This can be achived by moving the concatenate code in 
ComputePerspectiveTransform to the end of the function.

Also, when using the UserTransform this way the camera light will not 
follow, since it only depends on the ViewTransform. Unless the 
UserTransform is intended for an entierly different use, it would be 
nice to have the camera light transform depend on 
UserTransform*ViewTransform.

Eigil