Add function Bool_t IsScalingForRender() that returns true if length of base
  vectors is significantly different than unity.

* TGLPhysicalShape:
  Cache state of fTransform.IsScalingForRender() in a bool member.
  When this is true, enable automatic scaling of normals during rendering.

* TGLLogicalShape:
  Add static Bool_t fgIgnoreSizeForCameraInterest allowing a user to prevent
  RGL from hiding very small objects - at least a pixel is always drawn. One
  should invoke:
    TGLLogicalShape::SetIgnoreSizeForCameraInterest(kTRUE);


git-svn-id: http://root.cern.ch/svn/root/trunk@46372 27541ba8-7e3a-0410-8455-c3a389f83636