test_bug1001011(): Verify that

test_bug1001011():  Verify that

    s.join([t]) is t

for (s, t) in (str, str), (unicode, unicode), and (str, unicode).
For (unicode, str), verify that it's *not* t (the result is promoted
to unicode instead).  Also verify that when t is a subclass of str or
unicode that "the right thing" happens.