CREINS ( owner, part, transf, type, instnc, ifail )
===================================================

  Create instance.

Receives:
  KI_tag_assembly          *owner          --- owning assembly of new instance
  KI_tag_part              *part           --- part to be instanced
 <KI_tag_transform>        *transf         --- transform of instance
  KI_cod_tyin              *type           --- type of instance

Returns:
  KI_tag_instance          *instnc         --- new instance
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_wrong_transf           transform contains scale or reflection
  KI_anon_sub_part          instance of anonymous sub-part of stored part
  KI_cyclic_assy            instance would cause cyclic reference
  KI_not_in_same_partition  Owner and part are in different partitions

Description:
  CREINS creates a new instance of 'part' and attaches it to the assembly
  'owner'.

  If the new instance would cause the assembly graph to become cyclic (i.e. when
  creating an instance of P in A, and P or a sub-part of P is A) KI_cyclic_assy
  will be returned in 'ifail'.

  The part may not be unloaded (ENSTUN).

  We define the true-sub-parts of a stored (ENSTST) part S as those anonymous
  (ENSTAN) sub-parts of S reachable from S without encountering other stored
  parts (see OUPART for a description of all part states).

  If P is anonymous and is a true-sub-part of some stored part S then P may only
  be instanced from S or a true-sub-part of S. If this condition is not met
  KI_anon_sub_part is returned in 'ifail'.

  A copy of 'transf' is attached to the new instance.

  If a null tag is given for the transform, the transform field of the instance
  is left null and the system will act as if the instance has an identity
  transform attached.

  The transform must consist of translation and rotation only: if scaling,
  reflection or shearing is present KI_wrong_transf is returned in 'ifail'.

  The type given must a token in the range TYINxx. At present the only valid
  value is positive (TYINPS).

  Creating an instance is regarded as changing the owning assembly of the new
  instance but not the part that is instanced. If the assembly is new or
  modified no change of states will take place. If it is anonymous or stored its
  state will be changed to new and modified respectively. The effect of this
  change will be rippled up the parts graph.