yz/p4-py3, was Re: What's cooking in git.git (Feb 2020, #03; Wed, 12)

> * yz/p4-py3 (2020-01-15) 14 commits
>  . ci: also run linux-gcc pipeline with python3.5 environment
>  - git-p4: use python3's input() everywhere
>  - git-p4: simplify regex pattern generation for parsing diff-tree
>  - git-p4: use dict.items() iteration for python3 compatibility
>  - git-p4: use functools.reduce instead of reduce
>  - git-p4: fix freezing while waiting for fast-import progress
>  - git-p4: use marshal format version 2 when sending to p4
>  - git-p4: open .gitp4-usercache.txt in text mode
>  - git-p4: convert path to unicode before processing them
>  - git-p4: encode/decode communication with git for python3
>  - git-p4: encode/decode communication with p4 for python3
>  - git-p4: remove string type aliasing
>  - git-p4: change the expansion test from basestring to list
>  - git-p4: make python2.7 the oldest supported version
>
>  Update "git p4" to work with Python 3.
>
>  Hold.
>  The last step is too wasteful to run full tests twice.
>  cf. <20200122235333.GA6837@szeder.dev>
>  cf. <20200123175645.GF6837@szeder.dev>