Prefer time field in a GTFS-realtime StopTimeEvent.

The GTFS-realtime spec dictates that the time field should be preferred over delay if both are present, but OneBusAway's handling of the fields was inverted from the spec.
Merge pull request #87 from kurtraschke/gtfs-rt-delay-time

Prefer time field in a GTFS-realtime StopTimeEvent.