Git: Drop Git submodules, those are nasty anyway.
Squashed 'scripts/vagrant/shell-scripts/' content from commit 71f8025

git-subtree-dir: scripts/vagrant/shell-scripts
git-subtree-split: 71f80254c778bc59e30309ee02f5d546ea0299cd
Git: Subtree merge 'scripts/vagrant/shell-scripts'.

Use git-subtree to perform a merge at commit '848252e933' from
'git://github.com/StanAngeloff/vagrant-shell-scripts.git'.

Use:

    $ make update-vagrant-shell-scripts

To update the dependency.
Makefile: Add task to update Git subtrees.

Add a .gittrees file which helps keep track of what's going on and where
content comes from. That file is not (yet) supported by Git, but there
are several forks which can make use of it.