bug#13649: boobytrapped dired-do-async-shell-command question

[Juri Linkov]

>>   A command is running in the default buffer.  What to do? (k/c/r/h)

Or rather to model the prompt after `save-some-buffers-action-alist'
that asks "Save file? (y, n, !, ., q, C-r, d or C-h)" and ask:

  A command is running.  Kill it? (y, n, c, r, or C-h)

where the key `y' would mean to kill the running process, `c' - create
a new buffer, `r' - rename the buffer with the running process, and
`C-h' - help with the explanation of these options including `C-g':

  C-g to quit (cancel the whole command);

> BTW, one more useful option would be "run it when the current command
> finishes".

IIUC, this will require adding a queue of postponed commands, and also UI
to handle them (e.g. to remove a submitted command from the queue, etc.)