tests: fix up some import statements caught by Python 3 I'm curious how the import checker manages to be so much more pedantic in Python 3, but not enough to bother exploring. Differential Revision: https://phab.mercurial-scm.org/D5240

tests: replace `tac` reimplementation by `sort -r` `sort -r` is better code "formatter" than `tac` since it's stable. It's also portable so we don't need to reimplement it in Python. Differential Revision: https://phab.mercurial-scm.org/D5239

tests: work around `tac` not being portable Introduce a tac.py helper and use it. Sigh. Differential Revision: https://phab.mercurial-scm.org/D5238

revlog: give formatting to clang-format This has two lines that are poorly formatted, both right after PyObject_HEAD macros. It's possible that in the future there will be a feature to tell clang-format that a token includes an end-of-line character (in this case the ;), but for now I'm willing to live with two poorly-formatted lines in a struct definition in exchange for not thinking about how this file is formatted. Differential Revision: https://phab.mercurial-scm.org/D5234

revlog: add blank line in comment to help clang-format Differential Revision: https://phab.mercurial-scm.org/D5233

revlog: add a comment to help clang-format produce less-awful results Differential Revision: https://phab.mercurial-scm.org/D5232

py3: ratchet caught two more passing tests Differential Revision: https://phab.mercurial-scm.org/D5236

perf: add a lazydeltabase option to perfrevlogwrite The option controls if we'll test the provided delta first. This is the current default behavior for unbundle.

perf: add `storage` as possible source for perfrevlogwrite This source will use the stored delta.

perf: add `parent-smallest` as possible source for perfrevlogwrite This source will use the smallest of the possible diff against parent.