1377 - Blacklist dependencies in git

now ensure_dependencies.py add dependecies to .git/info/exclude. 
Please use something like this one: ` for repo_type in repo_types.iteritems(): if repo_type.istype(repodir): repo_type.ignore(target)`. This would allow to mix up SCM/VCS, which is exactly what some of us are doing already. (Though the `get_repo_type()` function should be aware of that anyway and ensure it defaults to `hg` if both `Git` and `Mercurial` report `true` for `istype()`.)