Dont use librd thread primitive
Fixed rd_kafka_destroy() resource cleanup (issue #20)
Added regression test harness
Added regression test for issue #20
Make sure messages in fligth are sent to other brokers in case of leader failure.

Move messages that are currently in flight (to the current toppar leader)
back on to the toppar message queue (prepend) so they are properly sent
to the new broker if a new one is elected.
Cosmetics
Proper -lrt linker flag on Linux