Add --retry_on_unknown_partition option as workaround to prevent
discards when moving a partition between brokers.

	modified:   src/bruce/bruce.test.cc
	modified:   src/bruce/bruce_server.cc
	modified:   src/bruce/config.cc
	modified:   src/bruce/config.h
	modified:   src/bruce/input_thread.test.cc
	modified:   src/bruce/kafka_proto/choose_proto.cc
	modified:   src/bruce/kafka_proto/choose_proto.h
	modified:   src/bruce/kafka_proto/v0/wire_proto.cc
	modified:   src/bruce/kafka_proto/v0/wire_proto.h
	modified:   src/bruce/kafka_proto/wire_protocol.h