correctly generate Java superclass constructor calls; don't replace owner when Java method is called via a Jet class

generate checkcast instruction for 'as' calls; use accessors for accessing fields of other instances of the same class

first step of refactoring code to generate 'this' expressions and receivers in ExpressionCodegen; correctly generate references to outer class properties in inner superclass constructor call

correctly handle ensureReceiverOnStack() when the expression is itself a receiver; use correct type when putting/storing fields

implementation classes implement JetObject; initial implementation of getTypeInfo() method and typeof operator