Comment 5 for bug 1182204

The situation is the following:
slot-layouts-compatible-p checks if the types are eq, and that obviously doesn't work when deftype is changed.
generate-slotd-typecheck caches a type-check function based on the type name, that's easy to fix, since it can cache (specifier-type type) instead.
But the first one is a bit trickier, it either needs to store the expansion of the type in the slot structure, or just treat any types, besides the primitve ones, as incompatible. I'm not sure which strategy is better to pursue.