The series is a nice refator and looks good to me.
Excerpts from Yuya Nishihara's message of 2017-02-19 02:44:51 +0900:
> # HG changeset patch
> # User Yuya Nishihara
> # Date 1487433610 -32400
> # Sun Feb 19 01:00:10 2017 +0900
> # Node ID c6dd20729bb3fd2f7745139c27488ce7279f13e1
> # Parent
# HG changeset patch
# User Yuya Nishihara
# Date 1487433610 -32400
# Sun Feb 19 01:00:10 2017 +0900
# Node ID c6dd20729bb3fd2f7745139c27488ce7279f13e1
# Parent 22722c297b33c2f68a8a34e0b0be0e6a9e0f4759
chg: refactor ui.system() to be partly overridden
Since fd598149112b changed the signatur