ds: Don't blow up for untracked files
ds: Don't blow up for untracked files

We were creating a `nil` project given input like:

  M some_file
  ? some_other_file

Which was later causing us to blow up.

Instead, copy the untracked files too (this is usually what you want,
as you probably want to test an in-development file that you haven't
added yet; if it's not what you want you can just `hg revert` it, and if
this turns out to be a nuisance I can revise that decision...).

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent