* lisp/dired-aux.el (dired-check-process): Transform the top-level
comment into a docstring.
(dired-shell-command): New command. This mirrors
`dired-check-process', but is more user-friendly for passing
arguments.
(dired-compress-file-suffixes): Allow to specify the command switches
along with input (%i) and output (%o) inside the PROGRAM part.
Add an entry for *.zip files, and update the entry for *.tar.gz files
to the new style. Update the docstring.
(dired-compress-file): When PROGRAM matches %i or %o, use the new
logic.
(dired-update-file-line): Avoid an error when at end of buffer.