Optimize host name completion in Tramp
* lisp/net/tramp-adb.el (tramp-adb-maybe-open-connection): * lisp/net/tramp-gvfs.el (tramp-gvfs-maybe-open-connection): * lisp/net/tramp-rclone.el (tramp-rclone-maybe-open-connection): * lisp/net/tramp-sh.el (tramp-maybe-open-connection): * lisp/net/tramp-smb.el (tramp-smb-maybe-open-connection): * lisp/net/tramp-sudoedit.el (tramp-sudoedit-maybe-open-connection): Throw `non-essential' at the beginning of the function. * lisp/net/tramp.el (tramp-handle-file-exists-p): * lisp/net/tramp-sh.el (tramp-sh-handle-file-exists-p): * lisp/net/tramp-sudoedit.el (tramp-sudoedit-handle-file-exists-p): Run only when host is connectable. This is due to host name completion, which shall be optimized. * lisp/net/tramp-smb.el (tramp-smb-do-file-attributes-with-stat) (tramp-smb-get-file-entries): Access connection buffer only after sending the command. * lisp/net/tramp.el (tramp-get-buffer, tramp-get-connection-buffer): New argument DONT-CREATE. (tramp-message): Use it. (tramp-get-mutex): Check, whether host is connectable. (tramp-file-name-handler): Set thread only when host is connectable. (tramp-connectable-p): Allow also VEC as argument. (tramp-completion-handle-file-name-completion): Do not expand directory.