o Major features (relay, infrastructure):
   - Implement a new inter-cmux comparison API, a global high/low watermark
     mechanism and a global scheduler loop for transmission prioritization
     across all channels as well as among circuits on one channel. This
     schedule is currently tuned to (tolerantly) avoid making changes
     in the current network performance, but it should form the basis
     major circuit performance increases.  Code by Andrea; implements
     ticket 9262.

 o Testing:
   - New tests for many parts of channel, relay, and circuit mux
     functionality.  Code by Andrea; part of 9262.