* I'm still going to try to include what is used in each module.
* At some point, I should implement these in the main project. It will
need more testing on the various compilers. It really needs to be
on-by-default everywhere. If it's off, then at least pch.h should be
included everywhere, to minimize configuration differences between my
checkout and other people's checkouts.
* There should be some way to configure it off to check whether includes
are correct.
* The change reduces build times from 27.6s to 15.2s on a single-core VM.
