Message 306802 - Python tracker

Also see https://bugs.python.org/issue1660500 for the original Python 3.0 change to hide the iteration variable.

While the test suite already covers some interesting scoping edge cases as result of that initial patch, I think one we're currently missing is the nested comprehension case:

    >>> [[x for x in range(1, i)] for i in range(2, 5)]
    [[1], [1, 2], [1, 2, 3]]