[Truffle] adapted Object#dup to conform to reference
[Truffle] Merge.
[Truffle] Dispatch nodes may now ignore visibility on method calls
[Truffle] Common default constructor for dispatch nodes.
[Truffle] - Implementing Class#superclass method.
[Truffle] - Allows using self as the superclass if self is a class.
[Truffle] - Added method getRubySuperClass method to DefineOrGetClassNode.

DefineOrGetClassNode: moving code that gets the superclass (or raise a
typeError) to a new method: getRubySuperClass().
[Truffle] - Showing Ruby stacktrace when running code outside of a
class/module context.
[Truffle] - A class definition raises a TypeError if inheriting from a metaclass.