Modify router thread implementation to support message rate limiting and
automatic topic creation.  Still need to modify dispatcher to support
automatic topic creation.

	modified:   src/bruce/msg.cc
	modified:   src/bruce/msg.h
	modified:   src/bruce/msg_rate_limiter.cc
	modified:   src/bruce/msg_rate_limiter.h
	modified:   src/bruce/router_thread.cc
	modified:   src/bruce/router_thread.h