control_flow: fixes for event whitelisting

two bugs fixed:
 - event.proceed for whitelisted events was immediately returning
   true, causing us to 'rush ahead' and screw up the timing. Now the
   scheduler checks for a new whitelisted() method, and then branches
   to a different scheduling strategy (essentially, just pretends the
   event happens exactly when predicted)
- typo in Replayer and peeker
     self.simulation.openflow_buffer.pass_through_whitelisted_packets
     said "...messages" but the flag in openflow_buffer is called "...packets"
Merge branch 'master' of github.com:ucb-sts/sts