c50b1b9ef6
VariationMerger is updated such that it accepts None list members in .mergeThings, and switches to correct sub-model. This means, it technically supports more than just a few masters missing GPOS. This allows for some within-GPOS differences to also be handled, though that's not well-studied or complete. Part of https://github.com/googlei18n/fontmake/issues/88 Part of https://github.com/fonttools/fonttools/issues/1355