RE: improve Dired menus

["Drew Adams" <drew.adams@oracle.com>]

I'm unfamiliar with the encryption commands, so in my proposal I left them in
the menu where they were. After looking at the code a bit, it seems there is a
bug (filed as #4703) - they should be in the Operate menu, not the Immediate
menu.

For my proposal, they would thus be in `Multiple', not `Single'. They each act
on the set of marked files (or the next prefix arg files).

This is another example of the mischievousness of such meaningless names as
"Immediate". Apparently, whoever added them to `Immediate' just figured "Hey,
they're immediate", which of course they are - like all commands.

Also in bug #4703: If these menu items do not apply to subdirectory lines, then
an appropriate :enable entry should be added to disable them for non-file lines.