Add support for automatic topic creation.  Discard per-topic batcher
contents on router thread shutdown.

	modified:   src/base/fd.h
	modified:   src/bruce/config.cc
	modified:   src/bruce/config.h
	modified:   src/bruce/discard_file_logger.cc
	modified:   src/bruce/discard_file_logger.h
	modified:   src/bruce/kafka_proto/v0/metadata_request_writer.cc
	modified:   src/bruce/kafka_proto/v0/metadata_request_writer.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
	modified:   src/bruce/metadata_fetcher.cc
	modified:   src/bruce/metadata_fetcher.h
	modified:   src/bruce/router_thread.cc
	modified:   src/bruce/router_thread.h