Resolution of B-2 not reflected in B-6 (aka covariant returns)

[Martin von Loewis]

I just tried to understand our scheme for covariant returns, and found
I couldn't. All I found was:

- there are different vtable entries for each different return type.
- at the end of issue B-2, it is explained that the exact definition
  is found in issue B-6.
- in issue B-6, it is explained that the resolution to that issue is
  found in the ABI layout document
- in the ABI layout document, there is no mentioning of covariant
  returns.

If desired, I can try to produce a draft.

Martin