Make println more Pythonic--in particular, print "None" for None (instead of "null").

Fix https://github.com/jdf/Processing.py-Bugs/issues/74
Improve logging of SketchRunner RMI handshake.
Improve reporting of internal errors by including legit java-space stack traces.
Implement constrain() in python.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/77.
Build 0364.