copies: do copy tracing based on ctx.p[12]copies() if configured This adds an option to do copy tracing in a changeset-optimized way. If the metadata is stored in filelogs, this is obviously going to be suboptimal. The point is that it provides a way of transitioning to changeset-stored metadata. Some of the tests behave a little differently, but they all seem resonable to me. The config option may very well be renamed later when it's clearer what options we want and how they will behave. When the test suite is run with --extra-config-opt to use the new copy tracing, all tests pass, besides test-copies.t (which fails in the same way as you can see in this patch). `hg debugpathcopies 4.0 4.8` reports 82 copies. With this option enabled, the only difference is this: -mercurial/pure/bdiff.py -> mercurial/cffi/bdiff.py +setup_bdiff_cffi.py -> mercurial/cffi/bdiff.py I believe that happened because it was renamed in different ways on different sides of a merge and the new algorithm arbitrarily prefers copies that happened on p1. The runtime is about 0.85 seconds with the old copy tracing and 5.7 seconds with the new copy tracing. That's kind of slow, but actually better than I had expected. Differential Revision: https://phab.mercurial-scm.org/D5991