tools.gitlibs.impl changes

[puredanger]

Just FYI, this project uses some internals of tools.gitlibs, and those internals have changed in the 2.x releases. Namely, the implementation now shells out to git and does not use jgit/jsch and there are many function differences in the internal impl namespace. So, just a heads up that if you update to the newer releases you'll need to modify your implementation too.