Address bug from Titanium Studio 'optimization':

When it optimizes stackmob-titanium.js, Titanium Studio changes the line that defines a variable to hold the given value of `params['error']` from

    var err = params['error'];

to simply

    params['error'];

...thus, when you get to the invocation of the `err` variable, `err` has no value.

I'm not sure, but I think the optimizer might think that `err` is supposed to refer to the caught exception in the `try/catch` block above. Perhaps it sees the `err` defined above as never being used, and that is why it removes the definition. 

When I renamed the variable meant to hold the original `params['error']` to `errorFn` the error handling code began working again. I'm submitting that as the patch to fix the undefined `err` problem.