The Equals method was using reference equality to compare ITypeReference instances.  Correct comparison of that type must use .Equals as equivalent generic values can be different objects.

This surfaced as a bug in determinism.  In the case we had an alias'd using where the target type was generic this Equals method came into play.  Based on whether we got a generic cache hit or not ended up changing the PDB output and as an effect the determinism id of the resulting assembly.

closes #7015