[PATCH 4 of 4 py3] manifest: use itertools.chain() instead of + for Python 3 compat

[Yuya Nishihara]

On Sun, 28 May 2017 21:43:05 -0400, Augie Fackler wrote:
> # HG changeset patch
> # User Augie Fackler <raf at durin42.com>
> # Date 1496021398 14400
> #      Sun May 28 21:29:58 2017 -0400
> # Node ID 0ecde7127f8816ca725282db684870ea8a8ad60f
> # Parent  d7743001547ef1de565717cebf7e88e31e60433c
> manifest: use itertools.chain() instead of + for Python 3 compat
> 
> This is all pure-Python code, so I'm not too worried about perf here,
> but we can come back and fix it should it be a problem.
> 
> With this change, the manifest code passes most unit tests on Python 3
> (once the tests are corrected with many b prefixes. I've got a little
> more to sort out there and then I'll mail that change too.

Great. Queued these, thanks.