Make it possible for customresponse check functions to get extra arguments, though they need to be declared in the XML.

We would fail if a global was defined with a non-jsonable value inside a jsonable one.  Now we don't/

Check functions now can only return serializable data, and 'ex' and 'got' weren't used later anyway.

Not sure why these had capital-I's in them, since the text just above shows lowercase-i's, and uppercase doesn't work properly.

A few places we used an option of 'imaginaryi', which isn't a real option.  Doesn't change any behavior.

Files are properly copied in both implementations of safe_exec, and a new python_path argument adds to the python path.