OUIDEN ( entity, id, ifail )
============================

  Output identifier of entity

    Can be called from the GO.

Receives:
  KI_tag_entity            *entity         --- entity whose id is required

Returns:
  KI_int_id                *id             --- id of specified entity
  KI_cod_error             *ifail          --- error code


Description:
  Returns the identifier 'id' of entity 'entity'.

  Any entity which is attached to a part has an identifier, which is unique
  within that part. This identifier is allocated automatically when the
  entity is attached to the part, and is maintained for as long as the entity
  is attached to the part; this applies even when the part is re-received into
  a later session. When an entity is transferred from one part to another,
  it will be allocated a new identifier appropriate to the destination part.
  In a boolean operation, for example, all entities within the target body
  will retain their identifiers, but those in the tool body will be allocated
  new identifiers appropriate to the target body.

  The identifier of an entity which is not attached to a part is returned as
  zero.