Fix bugs introduced by last commit

* contrib/sly-trace-dialog.el (sly-trace-dialog-mode): Don't call
`sly-navigation-mode'.
(sly-trace-dialog-mode-map): Don't rebind q twice. Don't inherit
from `sly-inspector-mode-map'.
Fix test failures and prepare for multi-threaded channels

* contrib/sly-mrepl.el (listener): Fix typo.

* contrib/swank-mrepl.lisp (create-mrepl): Don't mess with threads
here.
(create-mrepl): Use new CHANNEL-THREAD-ID.

* lib/lisp/swank.lisp (defpackage :swank): Don't export
channel-related stuff here.
(initialize-instance): Send :SERVE-CHANNEL message to responsible
thread here.
(dispatch-event): Use FIND-CHANNEL-THREAD in preparation for
multi-thread channels. Error when no suitable thread.
(defpackage :swank-api): Export CHANNEl-THREAD-ID.