[vtkusers] text orientation of vtkAxisActor label

[Denis Saussus]

I am using a vtkXYPlotActor object and would like to change the
orientation of the YaxisLabel text.  I thought of just applying a
vtkTransform.RotateX(90.) to the label actor but I cannot find a
way to the vtkAxisActor itself.  Is this the right way to accomplish what
i want (if so, how to make it work?) or am I missing something much
simpler?

Thanks in advance for any hints