tests: allow for a bonus newline in base64'd email payload Python 3 adds this newline, which is harmless. test-patchbomb.t now passes on Python 3. Differential Revision: https://phab.mercurial-scm.org/D4234

mail: be more cautious about bytes vs str for py3 compat It's suboptimal that we get a bytes on 2 and a unicode on 3, but it's easy to work with and I'm disinclined to change anything unless we start using some sort of type inferencer. Differential Revision: https://phab.mercurial-scm.org/D4233