Merge branch 'dd/bisect-helper-subcommand'

Fix a regression in the bisect-helper which mistakenly treats arguments to the command given to 'git bisect run' as arguments to the helper. * dd/bisect-helper-subcommand: bisect--helper: parse subcommand with OPT_SUBCOMMAND bisect--helper: move all subcommands into their own functions bisect--helper: remove unused options