Code review comment for lp://staging/~gary/juju-gui/fixDeltaFromChangeEdgeCase

*** Submitted:

optimize and fix databinding.deltaFromChange

This is a grabbag of three small changes. The biggest change is that I
did some optimizations of databinding.deltaFromChange and fixed an edge
case (with test). I also optimized _setupDependencies for that edge
case, added some documentation about bindings (so I could refer to it
myself), and optimized the bind/_bind pair a bit by removing redundant
calls to code that iterates over all bindings (they are now done once in
bind, rather than once per viewlet in _bind).

R=benji
CC=
https://codereview.appspot.com/13348056

https://codereview.appspot.com/13348056/