Channel-related robustness fixes

* contrib/swank-mrepl.lisp (create-mrepl):
MAYBE-REDIRECT-GLOBAL-IO must be called without any listener.

* contrib/swank-trace-dialog.lisp (:swank-trace-dialog): Use
:SWANK-API package.

* lib/lisp/swank.lisp (close-connection%): When closing channels
and listeners, ensure *EMACS-CONNECTION* is set.
(defpackage :swank-api): Don't use `eval'
Robustness fixes in sly.el

* sly.el (sldb-confirm-buffer-kill): Confirm buffer kill even if
`sldb-quit' errors.
(sly-update-connection-list): Make more robust when
`sly-connection-name' and `sly-lisp-implementation-type' aren't known yet.