[CM] question about pretty-print and object serialization

[bil at ccrma.Stanford.EDU]

I think the "..." truncation of vectors depends on the
(*s7* 'print-length) setting.  It's 12 for historical
reasons.  I think the :readable argument to object->string
(and the `W format option) came after write.scm and
pretty-print, so pretty-print might not be as complete
in that regard.