Make the tracker use the twisted callback
Twistify the bootstrap and allow it to be disabled
Refactor bootstrap resolution stuff so it works with the new twisted
callback, still some stuff pending to do, but its working just fine.
Port unit tests classes to the new twisted callback
Fix the tests
Community import cleanup
Further twistify the bootstrap process, untested
Skip looping resolution if bootstrap is disabled too
Make callback.call() thread safe.
This means TwistedCallback's contructor can't use it anymore to obtain
the reactor's thread ID hence from now on we need to make sure it always gets
instanced from there.