[PATCH 3 of 3 osx-packaging] osx: always purge build/mercurial before starting build

[Kevin Bullock]

> On Mar 20, 2017, at 17:03, Augie Fackler <raf at durin42.com> wrote:
> 
> # HG changeset patch
> # User Augie Fackler <augie at google.com>
> # Date 1490047124 14400
> #      Mon Mar 20 17:58:44 2017 -0400
> # Node ID 2f315db599ec7886b51a9d1ada7b5748ae2136dd
> # Parent  58e38cc8a32128436c27c90f431b150acd925024
> osx: always purge build/mercurial before starting build

Good stuff. Pushed, thanks.

pacem in terris / мир / शान्ति / ‎‫سَلاَم‬ / 平和
Kevin R. Bullock