[PATCH STABLE] tests-subrepo-git: make the "pwned" message output in a stable order

[Sean Farley]

danek.duvall at oracle.com writes:

> # HG changeset patch
> # User Danek Duvall <danek.duvall at oracle.com>
> # Date 1464309643 25200
> #      Thu May 26 17:40:43 2016 -0700
> # Branch stable
> # Node ID 821cafd65aac2b2199764acba0b1ede8d6e62b6e
> # Parent  89bba2beb03ea62e7fc8bcf3272e3cda1065ad89
> tests-subrepo-git: make the "pwned" message output in a stable order
>
> The "pwned" message from this test gets gets sent to stderr, and so gets
> emitted in different places from run to run in the rest of mercurial's
> output.  This patch forces the message to go to a specific file instead,
> whose contents we can examine in a stable point in the test's execution.

Seems fine to me.