Fix all existing tests

Also some extra sly-mrepl consistenty tweaks.

* sly-tests.el (arglist): Fix test to new SWANK protocol.
(sly-test-check-repl-forms): Fix test to wait for the MREPL to set
itself up properly.

* contrib/sly-mrepl.el (sly-mrepl--buffer-name)
(sly-mrepl--commit-buffer-name): More consistent mrepl naming
strategy.
(sly-mrepl-new): Use `sly-mrepl--buffer-name'. Don't insert "SLY"
version here. Call `sly-mrepl--commit-buffer-name'
(sly-mrepl-close-repls): Goto end of buffer before inserting
header line..
(sly-mrepl): Fix mrepl buffer finding.

* contrib/sly-mrepl.el (sly-mrepl--find-buffer): New function..
(sly-mrepl--find-create): Use `sly-mrepl--find-buffer'

* contrib/swank-mrepl.lisp (print-object mrepl): New method.
(create-mrepl): Insert "; SLY <version>" string remotely.
(revert-global-io-redirection): Check for NIL target.