split: close transaction in the unlikely event of a conflict while rebasing `hg split` *should* never result in conflicts, but in case there are bugs, we should at least commit the transaction so they can continue the rebase. One of our users ran into the regression fixed by D10120. They fixed the conflict and the tried to continue the rebase, but it failed with "abort: cannot continue inconsistent rebase" because the rebase state referred to commits written in a transaction that was never committed. Side note: `hg split` should probably turn off copy tracing to reduce the impact of such bugs, and to speed it up as well. Copies made in the rebased commits should still be respected because `hg rebase` calls `copies.graftcopies()`. Differential Revision: https://phab.mercurial-scm.org/D10164