SESTPA ( part, state, ifail )
=============================

  Set state of part.

Receives:
  KI_tag_part              *part           --- part to change
  KI_cod_enst              *state          --- desired new state of the part

Returns:
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_bad_state_combn        bad combination of old and new states

Description:
  SESTPA changes the state of the given part.

  Valid combinations of the part state and the desired state are given by the
  following table:

                Desired Part State (ENST..)

                   ST AN MD NW UN

      Given    ST        Y  Y-
      Part     AN           Y
      State    MD           Y-
               NW
               UN

  Where Y indicates a valid combination. All other combinations will return
  KI_bad_state_combn in ifail.

  For those combinations marked with a hyphen (i.e. stored or modified to new)
  the key of the part is discarded.

  If the original state of the part is stored or anonymous any stored or
  anonymous parts which instance it are also 'changed' to modified or new
  respectively, and any stored or anonymous parts which instance them and so on
  up the parts graph until a new or modified part is met. For example, the
  graph on the right shows the result of changing the part marked with a * in
  the graph on the left.

                           nw                     nw
                           |                      |
                           st                     md
                          /  \                   /  \
                         an  an                 nw  an
                        /  \                   /  \
                       an  an                 nw  nw
                        \  /                   \  /
                        *an                     nw
                         |                      |
                         an                     an

  This sequence of actions is called a 'state change ripple' and can be
  represented in pseudo code as:

    Ripple(P) =
      IF P is new or modified THEN RETURN
      IF P is anonymous or stored THEN
          SET P to new or modified
          FOR ALL parts Q which instance P
              Ripple(Q)

  A state change ripple may be caused by any function which 'changes' a part.