Merge branch 'nd/clone-detached'

* nd/clone-detached: clone: fix up delay cloning conditions push: do not let configured foreign-vcs permanently clobbered clone: print advice on checking out detached HEAD clone: allow --branch to take a tag clone: refuse to clone if --branch points to bogus ref clone: --branch=<branch> always means refs/heads/<branch> clone: delay cloning until after remote HEAD checking clone: factor out remote ref writing clone: factor out HEAD update code clone: factor out checkout code clone: write detached HEAD in bare repositories t5601: add missing && cascade