1377 - Blacklist dependencies in git

now ensure_dependencies.py add dependecies to .git/info/exclude. 
That's probably not the best choice, since `.hgignore` might be tracked in the repo and thus we're changing repo content here. Isn't there something similar to `.git/info/exclude` in Mercurial? Or some command similar to `git-update-index(1)`? If not, we may just leave the `Mercurial.ignore()` method empty..