Fix #28.

Squashed commit of the following:

commit 44346e18ed4b5cd8892c775787825d58471cefb5
Author: ko <git@yaksok.net>
Date:   Wed Oct 23 00:01:09 2013 -0700

    Fix #28 with PhysicsCache intermediate step.

commit b2e9b310acd0e30bbd4b125c23bb3656c6042167
Author: ko <git@yaksok.net>
Date:   Tue Oct 22 01:00:51 2013 -0700

    Begin the "wishful thinking" design phase of #28.