Merge branch 'uk/checkout-ambiguous-ref'

* uk/checkout-ambiguous-ref: Rename t2019 with typo "amiguous" that meant "ambiguous" checkout: rearrange update_refs_for_switch for clarity checkout: introduce --detach synonym for "git checkout foo^{commit}" checkout: split off a function to peel away branchname arg checkout: fix bug with ambiguous refs Conflicts: builtin/checkout.c