Another big step in the refactoring or Makefiles.

The recursive behavior is gone and we now use proper Makefile inclusions.
This brings full (and fast) dependency checking across the whole code base.
The output was also improved so that make -s gives something sensible.
At the same time, all constants declared in any Makefile have been grouped back to site.def and many simplifications have been done in the Imakefiles themselves.