Merge branch 'pw/rebase-abort-clean-rewritten' into maint

"git rebase --abort" used to leave refs/rewritten/ when concluding "git rebase -r", which has been corrected. * pw/rebase-abort-clean-rewritten: rebase --abort/--quit: cleanup refs/rewritten sequencer: return errors from sequencer_remove_state() rebase: warn if state directory cannot be removed rebase: fix a memory leak