Dependency comment.

It is thinking about this comment that I realized that all of CPM will
necessarily need to be subdirectory oriented. I don't like the
super-build approach (see:
http://www.cmake.org/pipermail/cmake/2011-October/046677.html), as it
appears very decentralized. I don't care about the IDE, but it does seem
very inconvienent in this day and age.