[PATCH v2 00/14] git-p4: python3 compatibility

This patchset adds python3 compatibility to git-p4.

While further 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

Changes since v1:
  - incorporate Ben's change on dropping usage of basestring
  - don't alias string types based on python verson
  - use feature detection instead of version checking to detect python3
  - CI patch now at end of series; needs further discussion
  - some general clean-up to commit messages

Ben Keene (1):
  git-p4: change the expansion test from basestring to list

Yang Zhao (13):
  git-p4: make python2.7 the oldest supported version
  git-p4: remove string type aliasing
  git-p4: encode/decode communication with p4 for python3
  git-p4: encode/decode communication with git for python 4
  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
  ci: also run linux-gcc pipeline with python3.5 environment

 azure-pipelines.yml |  11 ++
 git-p4.py           | 237 ++++++++++++++++++++++++++------------------
 2 files changed, 152 insertions(+), 96 deletions(-)