Don't use SetPropagatingDict in the built in console

Passing a dict subclass to eval is not supported in Python 2. This was causing
weird issues where the C-x would break the UI (I am not clear exactly how it
caused those issues).

The point of SetPropagatingDict is to combine globals and locals into a single
dictionary for things like code.InteractiveConsole and rlcompleter.Completer,
which take a single dictionary, but to allow changes to propagate, so that
assignments in the shell can modify global names. However, this is completely
unnecessary for the built in shell, as we call eval() ourselves, so we can
just pass the exact globals and locals dicts separately.

This fixes #166.