copies: get working copy parents from wctx, not dirstate, to make in-mem work Before this patch, `run-tests.py test-rebase-conflicts.t --extra-config-opt rebase.experimental.inmemory=1` would have some lines that say "searching for copies back to rev 3" changed to "... rev 1". I don't know of a better way of testing this patch than doing that manually. There are many other differences, so we're not ready to use #testcases syntax on the entire test-rebase-conflicts.t yet. Differential Revision: https://phab.mercurial-scm.org/D5596