Add tests for -replayLazily
Refactor -replayLazily to never dispose

This means not using -autoconnect, and aligns more closely to the
behavior of our other -replay… operators.
Refactor -autoconnect without private APIs
Merge pull request #759 from ReactiveCocoa/autoconnect-and-replay-changes

-replayLazily behavior changes, -autoconnect refactoring