CMake project reloading.

[Olivier J. G.]

PS. Re: "There's the other way with the buildset trying to build an
item that has been removed from the tree due to reloading"
Does that one still happen?... I thought the hack I made makes it so
that the build gets just gets canceled because the item no longer
exists, instead of crashing because the item no longer exists. Either
way though, that's an unfortunate fix.

PPS.
Sort order may be a very good explanation for this actually, since
it's imperative that the cpp be deleted before the h, which always
happens now, but may not have always happened before.