Handle port and domain in Tramp's password cache

Handle port and domain in Tramp's password cache

* doc/misc/tramp.texi (Password handling): Explain port and
domain handling in authinfo.

* lisp/net/tramp.el (tramp-process-actions, tramp-clear-passwd):
* lisp/net/tramp-gvfs.el (tramp-gvfs-handler-askpassword):
* lisp/net/tramp-sh.el (tramp-do-copy-or-rename-file-out-of-band)
(tramp-maybe-open-connection):
* lisp/net/tramp-smb.el (tramp-smb-handle-copy-directory)
(tramp-smb-handle-file-acl, tramp-smb-handle-set-file-acl)
(tramp-smb-maybe-open-connection): Handle also domain and port.