This patchset adds python3 compatibility to git-p4.

While some clean-up refactoring would have been nice, I specifically avoided
making any major changes to the internal API, aiming to have passing tests
with as few changes as possible.

CI results can be seen from this GitHub PR: https://github.com/git/git/pull/673

(As of writing, the CI pipelines are intermittently failing due to reasons
that appear unrelated to code. I do have python3 tests passing locally on
a Gentoo host.)

Yang Zhao (13):
  ci: also run linux-gcc pipeline with python-3.7 environment
  git-p4: make python-2.7 the oldest supported version
  git-p4: simplify python version detection
  git-p4: decode response from p4 to str for python3
  git-p4: properly encode/decode communication with git for python 3
  git-p4: convert path to unicode before processing them
  git-p4: open .gitp4-usercache.txt in text mode
  git-p4: use marshal format version 2 when sending to p4
  git-p4: fix freezing while waiting for fast-import progress
  git-p4: use functools.reduce instead of reduce
  git-p4: use dict.items() iteration for python3 compatibility
  git-p4: simplify regex pattern generation for parsing diff-tree
  git-p4: use python3's input() everywhere

 azure-pipelines.yml |  11 +++
 git-p4.py           | 195 ++++++++++++++++++++++++++++----------------
 2 files changed, 136 insertions(+), 70 deletions(-)

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2.21.0.windows.1