I created a comprehensive set of tests to check all the possibilities
that I listed in msg96319 and updated the patch for Object/exceptions.c.
Without patch all the test_*_with_overridden__str__ and
test_builtin_exceptions fail, both on 2.6 and on trunk, with the patch
all the tests pass.
The code in exceptions.c now does the equivalent of unicode(e.__str__())
instead of unicode(str(e)). If e.__str__() returns a non-ascii unicode
string, unicode() now shows the message instead of raising an error.