Another fix for external bug 2711 (over-eager conflicting class rejection).

The validateSuperDescriptors() test also checks for conflicts with
interface classes, and wasn't doing that quite right.  We need to compare
every method declared by an interface against the class' implementation
of it.  Methods implemented by superclasses are now tested in the context
of the superclass, not the current class.

This is a one-word fix + comments and new/updated tests.
6 files changed