Merge branch 'js/builtin-rebase-perf-fix'

Code clean-up with correction to make the reimplemented "git rebase" a more faithful rewrite of the original, which also regains performance. * js/builtin-rebase-perf-fix: built-in rebase: reinstate `checkout -q` behavior where appropriate rebase: prepare reset_head() for more flags rebase: consolidate clean-up code before leaving reset_head()