Some minor Tramp changes

Some minor Tramp changes

* lisp/net/tramp-adb.el (tramp-adb-handle-make-process):
Fix error message.

* lisp/net/tramp-cache.el (tramp-dump-connection-properties):
Remove `tramp-null-hop'.

* lisp/net/tramp-message.el (tramp-message, tramp-backtrace)
(tramp-error): Handle VEC being nil.

* lisp/net/tramp.el (tramp-null-hop): Add ;;;###tramp-autoload cookie.
Use pseudo method "local".
(tramp-file-name-unify): IF VEC is nil, set it to `tramp-null-hop'.
(tramp-set-completion-function): Support also functions with
METHOD as argument.
(tramp-get-completion-methods): Add argument HOP.
(tramp-completion-handle-file-name-all-completions): Use it.
(tramp-call-process-region): Set VEC if nil.