* New primitives `channel-register', `channel-unregister', and

* New primitives `channel-register', `channel-unregister', and
  `channel-registered?' allow registering of a set of channels that is
  to be watched for input at certain points.

* New primitive `channel-select-then-read' is like `channel-read', but
  returns #T if the given channel has no input but some other
  registered channel has some input instead.

* Primitive `x-display-process-events' now returns #T if there are no
  input events but a registered channel has some input.

* Primitive `make-subprocess' now permits the "inheritance" of
  Scheme's control terminal even when there is none.

* New primitive `process-status-sync-all' synchronizes the status of
  all subprocesses: it returns #T iff some status has changed since
  the last call to this primitive.