improve mechanism for generating version file

	modified:   SConstruct
	modified:   src/SConscript
	modified:   src/bruce/bruce.cc
	renamed:    src/bruce/version.cc.in -> src/bruce/build_id.c.in
	renamed:    src/bruce/version.h -> src/bruce/build_id.h
	modified:   src/bruce/config.cc
	modified:   src/bruce/kafka_proto/v0/mdrequest.cc
	modified:   src/bruce/mock_kafka_server/config.cc
	modified:   src/bruce/mock_kafka_server/inject_error/inject_error.cc
	modified:   src/bruce/scripts/gen_version
	modified:   src/bruce/simple_client/simple_bruce_client.cc
	modified:   src/bruce/web_request_handler.cc