Move minimal_satisfiable_subset to the logic module
Add an extra newline for readability
Try out minimal satisfiable subset algorithm that finds random subsets

It doesn't seem to help much in every case, although in some cases it helps a
lot.
Improve algorithm in minimal_unsatisfiable_subset to use a binary search

Unfortunately, we had to go back to dots instead of progress bars, because we
can't know how many iterations it will take.
Add XXX comment
Merge branch 'master' of github.com:conda/conda