Code clean-up.
* ab/bisect-cleanup:
bisect: no longer try to clean up left-over `.git/head-name` files
bisect: remove Cogito-related code
bisect run: fix the error message
bisect: verify that a bogus option won't try to start a bisection
bisect--helper: make the order consistently `argc, argv`
bisect--helper: simplify exit code computation