Check functions need access to course-local code also, so we need to save the python path from the problem setup, and use it for the check function.

From code review: the hash was shallow, so nested objects could have hashed differently when they didn't need to.

from non-ASCII unicode code submissions.

A new boolean on XModuleSystem that determines whether to allow execution of untrusted unsandboxed code.

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