minor cleanups to WRITE-SEQUENCE on octet-output-streams
minor cleanups to WRITE-SEQUENCE on octet-output-streams

We should be more consistent about respecting START and END.  These
arguments are also non-NIL always, so we needn't bother checking before
using them.

eadmund/ironclad,froydnj/ironclad,glv2/ironclad,sharplispers/ironclad