Ubuntu 16.04 can't compile latest changeset on default branch

[Marcin Kasperski]

> | python3 gendoc.py "hg.1.gendoc" > hg.1.gendoc.txt.tmp
> …
> | TypeError: Can't convert 'bytes' object to str implicitly
> …

Using legacy system (Ubuntu 16.04) I wouldn't try using python3 for hg.

Mayhaps you found some actual error, mayhaps not … but I doubt
Mercurial is noticeably tested against old versions of python3
(and I doubt it is worth it).