test-patchbomb.t: work around Python change d579866d6419 (issue4188) Python 2.7.7 and later (as well as some ubuntu/debian packages of 2.7.6) include a fix that makes the email module more pedantically correct for MIME boundaries, but this breaks our tests. We work around this by filtering the output of any 'hg email' invocations in the test that produce MIME messages.