Merge branch 'pb/bisect-helper'

An early part of piece-by-piece rewrite of "git bisect". * pb/bisect-helper: bisect--helper: `is_expected_rev` & `check_expected_revs` shell function in C t6030: explicitly test for bisection cleanup bisect--helper: `bisect_clean_state` shell function in C bisect--helper: `write_terms` shell function in C bisect--helper: rewrite `check_term_format` shell function in C bisect--helper: use OPT_CMDMODE instead of OPT_BOOL