Add attribute `original` on class Attribute
Add attribute `original` on class Attribute

It always points to the original Attribute object used for
instantiation. The original object points at itself.

With this field it is now possible to identify two attribute objects as
representing same attribute. The rule is: same original and same type
equals same attribute.

tony-o/rakudo,labster/rakudo,tbrowder/rakudo,tbrowder/rakudo,nbrown/rakudo,nbrown/rakudo,labster/rakudo,rakudo/rakudo,rakudo/rakudo,salortiz/rakudo,tony-o/rakudo,tony-o/rakudo,nbrown/rakudo,MasterDuke17/rakudo,rakudo/rakudo,labster/rakudo,softmoth/rakudo,labster/rakudo,tbrowder/rakudo,salortiz/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,tony-o/rakudo,labster/rakudo,salortiz/rakudo,nbrown/rakudo,tony-o/rakudo,MasterDuke17/rakudo,salortiz/rakudo,rakudo/rakudo,rakudo/rakudo,tbrowder/rakudo,softmoth/rakudo,tbrowder/rakudo,rakudo/rakudo,softmoth/rakudo,softmoth/rakudo,tony-o/rakudo,softmoth/rakudo,labster/rakudo,MasterDuke17/rakudo,nbrown/rakudo,salortiz/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,nbrown/rakudo,salortiz/rakudo