Resolve SF bug 1409403: email.Message should supress warning from uu.decode.

Resolve SF bug 1409403: email.Message should supress warning from uu.decode.

However, the patch in that tracker item is elaborated such that the newly
included unit test pass on Python 2.1 through 2.5.  Note that Python 2.1's
uu.decode() does not have a 'quiet' argument, so we have to be sneaky.

Will port to email 3.0 (although without the backward compatible sneakiness).