COPYEN ( oldent, newent, ifail )
================================

  Copy entity.

Receives:
  KI_tag_entity            *oldent         --- entity to be copied

Returns:
  KI_tag_entity            *newent         --- copy of entity
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_wrong_entity           can't copy entity of given type
  KI_part_not_isolated      copy would instance true-sub-part of stored part

Description:
  COPYEN returns a copy of 'oldent' in 'newent'. The types of entity which may
  be copied are:

  Assembly:
    'newent' will be an uninstanced copy of 'oldent'. The instances in 'newent'
    will be copies of those in 'oldent' but the parts they reference will not
    be copied. Any features and attributes attached to the assembly are also
    copied. The state of 'newent' will be new (ENSTNW).

    If 'oldent' is an unloaded (ENSTUN) assembly it is received before copying
    is attempted.

    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.

    A stored or anonymous assembly which instances true-sub-parts of a stored
    part may not be copied as this would cause the stored part to become
    unisolated. For example, the parts marked with a * may not be copied and
    KI_part_not_isolated will be returned in 'ifail'.

                  st
                   |
                  st*
                 /  \
                an* an*
                 \  /
                  an
                   |
                  st

  Instance:
    If 'oldent' is an instance of part P in assembly A then 'newent' will be
    a new instance of P in A with a copy of 'oldent's transformation. Any
    attributes attached to the instance are not copied.

  Body:
    'newent' will be an uninstanced copy of 'oldent'. Any features and
    attributes attached to the body will also be copied. The state of 'newent'
    will be new (ENSTNW).

    If 'oldent' is an unloaded (ENSTUN) body it is received before copying
    is attempted.

  Surface:
  Curve:
  Point:
    'newent' will be an copy of 'oldent' plus any underlying geometry. If
    'oldent' is construction geometry in a part 'newent' will also be
    construction geometry in the same part. Otherwise 'newent' will be
    orphaned. Any attributes attached to 'oldent' will not be copied.

  Transformation:
    'newent' is an orphaned copy of 'oldent'.

  List:
    'newent' is an orphaned copy of 'oldent'. In the case of a tag list the
    entities whose tags are in the list are not copied.

  Feature:
    'newent' will have the same members as 'oldent' and will be in the
    same part. Any attributes attached to 'oldent' will not be copied.


  If 'oldent' is not one of these types KI_wrong_entity is returned in 'ifail'.