[PATCH 09 of 19 pager] help: enable pager

[Yuya Nishihara]

On Sun, 19 Feb 2017 18:13:00 -0500, Augie Fackler wrote:
> # HG changeset patch
> # User Augie Fackler <augie at google.com>
> # Date 1486440561 18000
> #      Mon Feb 06 23:09:21 2017 -0500
> # Node ID f6f080904a6ecac993f137b92d50bf4991f8d07c
> # Parent  6dd615d163eb069405ba71fe968980d3340d4702
> help: enable pager

Good news: now --help can be paged!

Bad news: command error is hidden behind pager. Maybe we'll need to start
a pager before calling ui.warn() + commands.help_() ?