Fixes for POX dart

I'm not sure if you care anymore, Brandon, but this is a quick pass at getting riplpox working on recent versions of POX.  A quick test indicates that the POX/riplpox part seems to work now, though it appears there are incompatibilities with current versions of Mininet.  And, for that matter, with the cs244 branch?

With current Mininet, proactive didn't work.  I didn't look into this very far and instead tried the cs244 branch.

With the cs244 branch, I had to tweak some function names (addSwitch vs. add_switch, etc.) to get ripl to start, but then proactive mode seemed to work.