Merge branch 'js/checkout-detach-count'

When checking out another commit from an already detached state, we used to report all commits that are not reachable from any of the refs as lossage, but some of them might be reachable from the new HEAD, and there is no need to warn about them. By Johannes Sixt * js/checkout-detach-count: checkout (detached): truncate list of orphaned commits at the new HEAD t2020-checkout-detach: check for the number of orphaned commits