confusing behaviour in getModelFile()

[drnickisaac]

getModelFile() reads text files for different model options. I've long wanted to replace this with a proper meta-coded solution.

I've noticed that if regions are present, getmodelFile() ignores the contents of the text files and instead creates code on the fly. But it assembles the code using random walk model and other current options. If the user specified something different, there is no message to warn that the options have been overridden.

[drnickisaac]

I've done a temporary fix by adding a warning of this behaviour.