Zombie 2.0 compatibility

This PR gets the test suite passing against the current master branch of Zombie. I'll try and keep on top of it until Zombie gets a release, at which point we could look to merge it.

It does however skip two tests, that I don't think will be feasible, due to the way Zombie works. See #21

Included is a `ManualStartZombieServer`, that makes it a little easier to debug test cases etc.