Initial commit
Add 'extern/common/' from commit '5844c4627682f009fff8fc048793879c0f0a3064'

git-subtree-dir: extern/common
git-subtree-mainline: 3bf653b347c0cdf57a4f83bb6134af9913b96335
git-subtree-split: 5844c4627682f009fff8fc048793879c0f0a3064
Adds script to update externs