mail: document behavior of Python 3 test-notify.t (and possibly other tests) are failing on Python 3 because email.message.Message is now aware of encodings and attempts to roundtrip values with the specified message encoding. Python 2 doesn't perform this roundtripping. We have tests with non-ascii data being serialized to a message that claims to use ascii encoding. I /think/ Mercurial's behavior may be buggy here. But I'm not sure. I'm documenting the behavior so the next person who looks into this doesn't start from scratch like I did. Differential Revision: https://phab.mercurial-scm.org/D5714

notify: be more defensive aboute None values encoding.strtolocal is the identity function on Python 2 but an actual string manipulation routine on Python 3. In some cases, we were passing None, which caused Python 3 to barf. Let's change the code to react properly when the value is None. Differential Revision: https://phab.mercurial-scm.org/D5713

wireprotov2server: use our JSON encoder Python's json module doesn't like to encode bytes instances. This makes this code difficult to work with Python 3. We simply swap in Mercurial's JSON encoder to work around it. Differential Revision: https://phab.mercurial-scm.org/D5712

tests: add optional setsockopt() lines for Python 3 Differential Revision: https://phab.mercurial-scm.org/D5711

diffstat: support filenames with whitespaces on renames This is a follow-up patch to D5628. `line.split()` cannot get filenames with whitespaces as mentioned by @yuja. This patch replaces `split()` method with `slice`. Corresponding tests were also added. Differential Revision: https://phab.mercurial-scm.org/D5709

largefiles: avoid walking full manifest When using treemanifest, diffs between two manifests can often be much cheaper than iterating the full manifests (because common subtrees are skipped). Differential Revision: https://phab.mercurial-scm.org/D5644