Proper fallthrough for -X "topic." properties
Periodic metadata requests could occassionally be flooded.
Add support for auto-creating topics on broker (issue #22)

This requires "auto.create.topics.enable=true" to be configured on the
brokers.

The automatic topic creation trigger (a topic-specific metadata request)
is performed every second, as well as immediately when a new topic is added
if at least one broker is up.
Clarified comment