NEGENT ( entity, ifail )
========================

  Negates (reverses) an entity

Receives:
  KI_tag_entity            *entity         --- entity to be negated

Returns:
  KI_cod_error             *ifail          --- failure code

Specific errors:
  KI_unsuitable_entity      unsuitable entity
  KI_bad_sharing            entity is a dependent of another geometric entity
                            dependent is owned by more than one geometric entity
  KI_is_attached            geometric entity is attached to topology
  KI_general_body           general body

Description:
  Negates (reverses) a curve, surface or body.

  Operations performed
  . Negating a curve reverses the curve direction.
  . Negating a surface reverses the surface normal.
  . Negating a body reverses the normals of all non-rubber faces.

  If the entity is a curve or surface it must not be attached to any topology.
  Furthermore curve and surface entities must not be dependents of any other
  geometric entities.

  This function is not at present supported for general bodies.