This is more RFC compliant (see issue) and fixes a problem with
signature verifiers rejecting the part when signed.  There is some
amount of backward compatibility concern here since it changes
the output, but the RFC issue coupled with fixing the problem
with signature verifiers seems worth the small risk of breaking
code that depends on the current incorrect output.

Once Barry and the email-sig have a working new version
we'll add it back.
If it doesn't make the 3.0a deadline (release August 31), too bad.

(i.e. email.test), so move the guts of them here from Lib/test.  The
latter directory will retain stubs to run the email.test tests using
Python's standard regression test.

test_email_torture.py is a torture tester which will not run under
Python's test suite because I don't want to commit megs of data to
that project (it will fail cleanly there).  When run under the mimelib
project it'll stress test the package with megs of message samples
collected from various locations in the wild.

email/test/data is a copy of Lib/test/data.  The fate of the latter is
still undecided.

suite.  Note that other tests can put input data in this directory.