Added superCtor to ctor.super_ instead superCtor.prototype.

This way let's us do deep comparison between object instances.

I have a suggestion for the sys.inherits function. Today it's impossible to
deep comparison between instance and class.

Take this snippet for example:

function ClassA() {}
function ClassB() {}

sys.inherits(ClassB, ClassA);

var instance = new ClassB();

The instance variable inherits from ClassA but we can't check it (which is
useful sometimes). You can compare the instance against ClassB
(instance.constructor == ClassB) but we can't compare it deeper
(instance.constructor.super == ClassA). The committed change simply assign
super to the super constructor instead of the super prototype.

I can't see any problem with this fix. You can still get the super constructor
by calling super_.prototype.