Dealing with PyFuncs more robustly.

Not sure it will work with icpc though.
Missing a + .
Added logging for creation of ops/signals.
Added an LIFRate test.
Fixed LIF rate math.

Now all nengo tests pass except the ALIF test (and my own LIF test,
which isn't exactly correct at the moment.
Fixed testing, mpi plots stored in correct dir.

Stores plots in the same directory that the main nengo tests store their
plots in. Does this using nengo.utils.testing.Plotter.
Makefile should work on both platforms.

GPC and ubuntu.