Pairing glyf/loca causes fonts to fail OTS and thus be rejected by Chrome

I think I have hit a problem with the glyf/loca pairing (implemented in
woff2 HEAD). Currently HEAD pairs glyf/loca in the woff2 file and re-orders
(to otspec order) when decoding.

The latest OTS re-orders tables and accepts this just fine. However, legacy
OTS (including version in browser) reject a woff2 encoded in the new
ordering (ERROR: table directory not correctly ordered).

As a result, if you encode a woff2 using https://github.com/google/woff2 at
HEAD it will not render in Chrome. I think this means the ordering
effectively represents a breaking wire format change.

Perhaps we should make the glyf/loca pairing requirement only for
collections and say regular woff2 table directories should order in the
otspec recommended order? Other ideas?