IDATEN ( entity, type, attrib, ifail )
======================================

  Enquire the attribute of a given type attached to an entity.

    Can be called from the GO.

Receives:
  KI_tag_entity            *entity         --- entity in which to look
  KI_tag_attrib_def        *type           --- type of attribute to look for

Returns:
 <KI_tag_attribute>        *attrib         --- attribute
  KI_cod_error             *ifail          --- error code

Specific errors:
  KI_wrong_entity           'entity' cannot own attributes of 'type'

Description:
   Returns the attribute of 'type' attached to 'entity', or the null tag if
  there is no such attribute.  If the given 'entity' is not permitted to own
  an attribute of the given 'type', KI_wrong_entity is returned in 'ifail'.

   If IDATEN is used for attributes of class RQAC06 or RQAC07, it will only
  return one attribute, even if several are present.