1.0.32.16: external-format restart enhancements

1.0.32.16: external-format restart enhancements

* OUTPUT-REPLACEMENT restart for fd-stream external-formats, taking a
  string designator argument and attempting to encode that instead of the
  erroneous output;

* fixes for the FORCE-END-OF-FILE fd-stream external-format restart, using
  a somewhat involved call / return protocol for communicating out-of-band
  information between output routines and drivers;

* INPUT-REPLACEMENT restart for fd-stream external-formats, again with
  complicated out-of-band information communication.  This also interacts
  with UNREAD-CHAR;

* fix the ATTEMPT-RESYNC restart (and similar) at or near the end of file,
  ensuring that there is always a valid CATCH tag to be THROWN to;

* fix a double-error case in the USE-VALUE restart for unibyte octet
  conversions;

* bandage fix for mb-util decoding-error USE-VALUE restart -- there's more
  factoring to be done, but this fixes lp #314939