Merge branch 'sb/checkout-explit-detach-no-advice' into maint

"git checkout --detach <branch>" used to give the same advice message as that is issued when "git checkout <tag>" (or anything that is not a branch name) is given, but asking with "--detach" is an explicit enough sign that the user knows what is going on. The advice message has been squelched in this case. * sb/checkout-explit-detach-no-advice: checkout: do not mention detach advice for explicit --detach option