* Prevent IsDuplicate from panicing on wrong Rrtype
* Replace the isDuplicateRdata switch with an interface method
This is substantially simpler and avoids the need to use reflect.
* Add equal RR case to TestDuplicateWrongRrtype
* Move RR_Header duplicate checking back into IsDuplicate
This restores the previous behaviour that RR_Header's were never
equal to each other.
* Revert "Move RR_Header duplicate checking back into IsDuplicate"
This reverts commit a3d7eba50825d546074d81084e639bbecf9cbb57.
* Run go fmt on package
This was a mistake when I merged the master branch into this PR.
* Move isDuplicate method to end of RR interface