ENBXEN ( entity, entbox, ifail )
================================

  Enquire box containing the specified entity.

Receives:
  KI_tag_topology          *entity         --- entity whose box is required

Returns:
  KI_dbl_box                entbox[6]      --- box containing entity
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_system_error           
  KI_empty_body             body has no faces, edges, or vertices
  KI_empty_assy             assembly instances no bodies
  KI_missing_geom           entity has missing point geometry
  KI_wrong_entity           entity is of incorrect type

Description:

  The entity must be an assembly, body, face or edge.

  The coordinates of the opposite corners of a rectangular box
  with sides parallel to X, Y and Z axes are returned. The box will
  contain the specified entity and will usually be close to the
  minimum possible size, but this is not guaranteed.

  Element zero of array 'entbox' will contain the minimum X coordinate
  of the box, element one the minimum Y, element two the minimum Z,
  element three the maximum X and so on. On failure, all elements of
  'entbox' will be set to zero.

  If edge or face geometry is missing the entity will still be boxed
  ignoring those edges and faces. If any point geometry is missing
  then the boxing will fail.

  An attempt to box an assembly which instances no bodies will fail.

  If a body is empty the ifail KI_empty_body will be returned.