SAVMOD ( part, keylen, key, ifail )
===================================

  Save model in archive.

Receives:
  KI_tag_part              *part           --- part to transmit
  KI_int_nchars            *keylen         --- length of key
  KI_chr_key                key[keylen]    --- key of part

Returns:
  KI_cod_error             *ifail          --- failure indicator

Specific errors:
  KI_bad_text_conversion    invalid value for text output
  KI_applio_not_registered  application i/o functions not registered
  KI_disc_full              disc full
  KI_file_access_error      error writing or closing the transmit file
  KI_cant_open_file         error opening the transmit file
  KI_schema_access_error    error opening, closing or writing the schema file
  KI_modified_sub_part      part has modified sub-part
  KI_part_not_isolated      part not isolated
  KI_already_saved          part is already stored in archive
  KI_key_in_use             key already used in archive
                            can't transmit modified part with same key
  KI_bad_key                invalid key syntax

Description:
  SAVMOD transmits 'part' and its true-sub-parts into the archive with the given
  'key'.

  The part must be new or modified (by definition stored, anonymous and unloaded
  parts are already in the archive).

  Whether parts are transmitted in text or in binary depends on the value of the
  SLIPBT interface parameter (see SEINTP for details).

  If 'part' is modified 'key' must not match the key already attached to the
  part. In fact if the key matches the key of any other part in memory
  KI_key_in_use will be returned in 'ifail'. This error code may also be
  returned if the key is already used in the archive.

  We define the true-sub-parts of a part P to be all sub-parts of P which can
  be reached without encountering a keyed (i.e. stored, unloaded or modified)
  part.

  The part and all true-sub-parts of the part are transmitted into the archive
  under the same key. When transmitted the part is changed to stored and all
  true-sub-parts are changed to anonymous. For example (the parts marked * are
  the true-sub-parts of P, and ST represents a stored part and its
  true-sub-parts):

      Before transmit of P              After transmit of P

           P->md                    P->st                   ST
             /  \                     /  \                 /  \
           *nw *nw                   an  an               ST  ST
           /  \/  \                 /  \/  \                 /  \
         *nw *nw  ST               an  an  ST      OR       ST  ST
         /       /  \             /       /  \                \/
        ST      ST  ST           ST      ST  ST               ST
                  \/                       \/
                  ST                       ST

  If the part is to be transmitted it must be the root of an isolated sub-graph
  which references only stored or unloaded parts. If these conditions are not
  met the state changes would cause EITHER a new or modified part to become
  a sub-part of a stored part OR a stored part to become the root of a
  non-isolated sub-graph. For example:


      Before transmit of P      After transmit P is stored but has modified
                                sub-part and thus SAVMOD will fail returning
                                KI_modified_sub_part in 'ifail'.

           P->md                    P->st
             /  \                     /  \
            nw  nw                   an  an
           /  \/                    /  \/
          nw  md                   an  md


      Before transmit of P      After transmit P is stored but is not root of
                                isolated sub-graph and thus SAVMOD will fail
                                returning KI_part_not_isolated in 'ifail'.

           P->md                    P->st
             /  \                     /  \
            nw  nw  md               an  an  md
           /  \/  \ /               /  \/  \ /
          nw  nw  nw               an  an  an