* doc/misc/tramp.texi (Extension packages): Explain how to use own
format specifiers.
* lisp/net/tramp.el (tramp-expand-args): Make DEFAULT argument
optional. Handle also ARGS being an atom.
(tramp-handle-make-process):
* lisp/net/tramp-container.el (tramp-skeleton-completion-function):
* lisp/net/tramp-sh.el (tramp-ssh-or-plink-options)
(tramp-maybe-open-connection):
* lisp/net/tramp-sshfs.el (tramp-sshfs-handle-process-file):
Call `tramp-expand-args' for `tramp-login-program'.