Merge branch 'mr/bisect-in-c-3'

Rewriting "git bisect" in C continues. * mr/bisect-in-c-3: bisect--helper: retire `--bisect-autostart` subcommand bisect--helper: retire `--write-terms` subcommand bisect--helper: retire `--check-expected-revs` subcommand bisect--helper: reimplement `bisect_state` & `bisect_head` shell functions in C bisect--helper: retire `--next-all` subcommand bisect--helper: retire `--bisect-clean-state` subcommand bisect--helper: finish porting `bisect_start()` to C