* Add mechanism to encapsulate one port in another, and to build

* Add mechanism to encapsulate one port in another, and to build
  wrappers around selected operations on the encapsulated port.

* Use new encapsulation mechanism to reimplement transcript facility
  so that each transcript is associated with a particular REPL.
  Previously the transcript was directly associated with the console
  port.

  This change is the goal of all of the port changes from this past
  week.  (I'm a little surprised at the depth of changes required.)

  This has the side effect of increasing modularity, since the
  transcript code is now concentrated in one file rather than being
  integrated into the console port.

* Export procedure OUTPUT-PORT/FRESH-LINE to the global environment.
  This was an oversight from previous changes.