[PATCH 1 of 2 pager-followup] help: avoid mutating passed-in `keep` list in `formattedhelp`

[Yuya Nishihara]

On Wed, 08 Mar 2017 18:43:20 -0500, Augie Fackler wrote:
> # HG changeset patch
> # User Augie Fackler <augie at google.com>
> # Date 1489015893 18000
> #      Wed Mar 08 18:31:33 2017 -0500
> # Node ID 767afd48cd786deb5bebd542f739a18640c50038
> # Parent  8dcc7582ec043d04d800a54a579f0f25ee7b44f4
> help: avoid mutating passed-in `keep` list in `formattedhelp`

Queued these, thanks.