EventLoop accepts reactor factory instead of reactor itself, in order to
allow delaying importing the reactor.
Delay importing the reactor until Crochet is setup, so that
daemonization isn't broken (workaround for http://tm.tl/7105).
Changelog entry.
Merge pull request #47 from itamarst/import-reactor-later-45

Import reactor in crochet.setup()/no_setup(), rather than immediately.

Fixes #45