Merge branch 'pk/rebase-in-c-5-test'

Rewrite "git rebase" in C. * pk/rebase-in-c-5-test: builtin rebase: error out on incompatible option/mode combinations builtin rebase: use no-op editor when interactive is "implied" builtin rebase: show progress when connected to a terminal builtin rebase: fast-forward to onto if it is a proper descendant builtin rebase: optionally pass custom reflogs to reset_head() builtin rebase: optionally auto-detect the upstream