Be more willing to use an unsuitable circuit for exit.

Be more willing to use an unsuitable circuit for exit.

Specifically, there are two cases: a) are we willing to start a new
circuit at a node not in your ExitNodes config option, and b) are we
willing to make use of a circuit that's already established but has an
unsuitable exit.

Now we discard all your circuits when you set ExitNodes, so the only
way you could end up with an exit circuit that ends at an unsuitable
place is if we explicitly ran out of exit nodes, StrictNodes was 0,
and we built this circuit to solve a stream that needs solving.

Fixes bug in dc322931, which would ignore the just-built circuit because
it has an unsuitable exit.