SEUFEN ( tag, ufdval, ifail )
=============================

  Set user field of entity

Receives:
  KI_tag                   *tag            --- tag whose user field
                                           --- is to be set
  KI_int_ufdval             ufdval[]       --- user-field value:
                                           --- array length is the user-field
                                           --- size set by STAMOD

Returns:
  KI_cod_error             *ifail          --- error code

Specific errors:
  KI_not_a_tag              'tag' is not valid
                            'tag' is dead world
  KI_no_user_fields         user fields are not available

Description:
  The user field of 'tag' is set to the value given in array 'ufdval'.