[PATCH 4 of 4] copy: add flag for disabling copy tracing

[Augie Fackler]

On Tue, Feb 3, 2015 at 11:50 AM, Pierre-Yves David
<pierre-yves.david at ens-lyon.org> wrote:
> I believe the main motivation for this patch was extremely inflated by a
> performance regression in 3.3-rev. Now that the regression is fixed I think
> it would be wiser to not disable this important Mercurial feature.

Sure, but it probably makes sense to skip this step when we know it's
irrelevant, which will be cheap RSN.