Bring sim_npy back up to date with nengo

Tests are currently passing using nengo at this point:

commit e69afe1dc6c1b00579640ce6cdb6fa4156c180e5
Author: James Bergstra <james.bergstra@gmail.com>
Date:   Fri Dec 13 13:10:13 2013 -0500

    fix: TestSimulator to use self.Simulator

The hash will be broken by the rebase onto master if that gets to master,
but the date and message should help find it.