CREXSU ( profil, direct, smplfy, extsur, ifail )
================================================

  Create an extruded surface

Receives:
  KI_tag_curve             *profil         --- curve to be extruded
  KI_vec_direction          direct         --- extrusion direction vector
  KI_cod_logical           *smplfy         --- simplification flag

Returns:
  KI_tag_surface           *extsur         --- resulting extruded surface
  KI_cod_error             *ifail          --- error code

Specific errors:
  KI_impossible_sweep       Cannot determine extruded geometry
  KI_unsuitable_entity      Not one of the allowed curve types
  KI_invalid_geometry       Invalid curve

Description:

  This function creates an extruded or swept surface.

  The curve 'profil' is extruded along the direction vector 'direct', the
  new surface being the envelope of the curve.

  If 'smplfy' is KI_false then the function will always return a surface
  of type TYSUSE. If 'smplfy' is KI_true then, if possible, the function
  will return an analytic surface which is equivalent to the extruded
  surface. For example, an extruded line is almost always equivalent to
  a plane.

  The curve must be of one of the following types:

  line
  circle
  ellipse
  B-curve

  A self intersecting surface may be returned, but it is not possible to
  sweep a line along its own direction vector.

  If 'profil' is not an orphan, the resulting surface will be created as
  construction geometry in the owning part. A curve which is a dependent of
  another entity may be extruded - for example, a single curve may be the
  underlying curve of two swept surfaces.