cleanup: define output-stream and input-stream with defclass
cleanup: define output-stream and input-stream with defclass

We don't use DEFINE-PROTOCOL-CLASS, because that would define predicates which
in turn would overwrite functions OUTPUT-STREAM-P and INPUT-STREAM-P which are
part of the gray stream protocol.

Both protocol classes are only hinted by the specification.

slyrus/mcclim,slyrus/mcclim