The process for nest membership validation and the type of exception thrown has been updated.
  - same package check is first
  - throw IncompatibleClassChangeError instead of IllegalAccessError

Update all tests

Spec no longer precludes duplicate entries in NestMembers attribute.

Spec allows a reference to self in the NestMembers attribute

Spec precludes a reference to self in NestHost attribute

Add tests for self-referential attributes: nesthost->this; nestmembers->this

Add tests for duplicate NestMembers entries.

NOTE: These changes do not include the JVMS invokeinterface changes that do not relate directly to implementing nestmates. Those changes are still under discussion.