Update imports for renamed modules.
Stopped using dict.iter*.

Since performance isn't a primary concern, the non-iterable versions
will do just fine on Python 2.
Allow repeated iteration on DebugToolbar.panels.
Ensure _quote_params returns a list.

This fixes a few test failures.
Replace assertEquals by assertEqual.
Update introspection code.
Update usage of the threading module.
Implement method replacement for Python 3.

Python 3 doesn't have unbound methods.
Remove dead code.

These features were still tested, but they weren't used anywhere.