Bug: make sure parent faces are always inherited

[Overdr0ne]

From my commit: The face-attribute documentation says:

To ensure that the return value is always specified and absolute, use a value of default for INHERIT; this will resolve any unspecified or relative values by merging with the default face (which is always completely specified).

Why they didn't just make that the default, I don't know for sure, but maybe they didn't have inheritable faces before, so had to do it this way to maintain backward compatibility.

[Overdr0ne]

I'll make the same changes on the relevant parts of my other pulls if you accept this.