Make output redirection slightly more robust.

* swank.lisp (:swank): No need to export STOP-PROCESSING
(define-channel-method :teardown): Move teardown method here.
(initialize-instance): Don't take MAKE-OUT-STREAM and MAKE-IN-STREAM.
(close-listener): New method. Closing a listener just removes it
from the listener queue.
(close-connection%): Also close all listeners.
(defpackage #:swank-api): Export CLOSE-LISTENER, don't export
STOP-PROCESSING.

* contrib/swank-mrepl.lisp (mrepl): No longer pass :MAKE-OUT-STREAM and
:MAKE-IN-STREAM.
(create-mrepl): Pass :OUT and :IN streams here.
(define-channel-method :teardown): move to swank.lisp
(open-dedicated-output-stream,make-mrepl-output-stream): Take an ID as input, not an MREPL.
(init-global-stream-redirection): No need to check
(maybe-redirect-global-io): Use WITH-LISTENER to warn new REPL of
redirection change.
(close-channel): Explicitly close listener, which does not close
automatically when channel does.
Remove all contribs that depended on previous REPL implementation.

Might add them again as third party contribs.

* contrib/sly-asdf.el: Removed
* contrib/sly-banner.el: Removed
* contrib/sly-clipboard.el: Removed
* contrib/sly-media.el: Removed
* contrib/sly-motd.el: Removed
* contrib/swank-clipboard.lisp: Removed
* contrib/swank-media.lisp: Removed
* contrib/swank-motd.lisp: Removed
* contrib/test/sly-repl-tests.el: Removed
Properly ignore ChangeLog files