Add 'interposition/' from commit 'e0a6f66a20e5aa7d17119c5b6d9982e7c025efc5'

git-subtree-dir: interposition
git-subtree-mainline: ab07580206d4eec1dc5d9bec047b6339fb03e1d1
git-subtree-split: e0a6f66a20e5aa7d17119c5b6d9982e7c025efc5
README.