I'm getting some neat results by changing graph testing over to using pre-compiled headers
Shout out to Rene Rivera for helping me get this stuff together.
I'm getting some useful results out of changing to using pre-compiled
headers. There isn't the speed-up I expected, but it has actually
turned out useful for finding out incorrect header inclusion patterns
and will certainly be making the code more reliable. This is something
that we ought to consider trying more broadly in the project.