These two related PRs are all about remembering where a macro is expanded. 
Worse, we've got two competing goals -- the real location of the expansion, for 
__LINE__, and the virtual location of the expansion, for diagnostics.

There seems to be no way to unify the two competing goals.  If we simply "fix" 
the first, we break the second.  Therefore, I resort to passing down both 
locations.

Ok?


r~