rebase: disable `inmemory` if the rebaseset contains the working copy As described in the comment, rebasing the working copy parent with in-memory merge, and then updating to the new commit, isn't much faster because of the extra overhead of uppdating. Best to leave it off in that case. This commit makes deploying in-memory merge via an extension easier, because you can just set `inmemory=True` based on some config or probability, and this will turn off the cases where it's not desired. Differential Revision: https://phab.mercurial-scm.org/D1616