CREREF ( posn, normal, transf, ifail )
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  Create a reflection transformation.

Receives:
  KI_vec_position           posn           --- position on plane
  KI_vec_normal             normal         --- normal direction

Returns:
  KI_tag_transform         *transf         --- reflection transformation
  KI_cod_error             *ifail          --- failure code


Description:
  Calculates a transformation matrix that, when applied to an entity,
  causes it to be reflected in the plane defined by the given position and
  normal.