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.