Control current time with now parameter in trip_optimizer - this lets the test harness be deterministic, and reuse old, recorded VCR cassettes for speed.
Remove debugging puts, added more detailed error message in Schedule class
Put hardcoded times in schedule_spec - this allows the pre-recording of VCR permanently. Also chanted to record: :once, so anytime the fixed date is changed, this will break tests (but tests will all be faster the rest of the time!)
Hardcoded @now in trip_optimizer_spec - again, for pre-recording of VCR permanently