With interactive trackdown, the user operates as both the initialization and test command.  He provides 
the results by answering prompts.

An example session might look like this:

  $ darcs trackdown --interactive
  Tracking down interactively.
  Code to be tested is in /tmp/trackingdown-2
  Does this version work correctly? [Ynq] n
  Trying without the patch:
  Thu Mar 15 16:35:18 MDT 2012  Michael Hendricks <michael@ndrix.org>
    UNDO: Style and error message clean up for patch733
  Does this version work correctly? [Ynq] n
  Trying without the patch:
  Fri Mar  9 16:53:02 MST 2012  Andreas Brandt <andreas.brandt.de@googlemail.com>
    UNDO: Tidy up wspfr
    Some style improvements and renaming variables to CamelCase
  Does this version work correctly? [Ynq] y
  Success!

Had the user answered 'q' at any of the prompts, the trackdown would have stopped immediately.

Original mailing list discussion: http://lists.osuosl.org/pipermail/darcs-users/2012-March/026413.html

One suggestion was to use a git-style trackdown.  That would be the first darcs command with such 
behavior, so it would need broad user discussion first.  It's probably also harder to implement 
considering the prompting infrastructure we already have.