(shell-dynamic-complete-functions): New variable.

(shell-dynamic-complete-functions): New variable.
(shell-mode): Use it to set comint-dynamic-complete-functions.

(shell-mode-map): Define menu-bars for command,
variable and directory completion/expansion.

(shell-get-current-command, shell-after-partial-filename): Functions deleted.

(shell-dynamic-complete-environment-variable,
shell-replace-by-expanded-directory): New commands.
(shell-match-partial-variable,
shell-dynamic-complete-as-environment-variable): New functions.