Calling Matlab inside a Python fitting function called by Matlab causes a hang

[mducle]

The Matlab computational engine is inherently serial. In the case here we have Python calling a fitting function in Matlab which requires evaluating a Python model function. The Matlab function yields execution to Python but waits until Python finishes; in the mean time, if the Python function then tries to call Matlab, this causes the program to wait until the Matlab fitting function finishes, causing a deadlock.

We should either try to:

1. Detect if Matlab is being called from a Python function and give an error
2. Try to implement some kind of two way communications / server client interface in call.m.

Option 1 is likelier to be much easier...