Object now has virtual get_own_property() and put_own_property() member
functions that can be overridden to provide custom behavior.
We use these virtuals to move Array-specific access behavior to Array.
This function is ultimately supposed to be generic and allow any |this|
that has a length property, but for now it only works on our own Array
object type.
I'm not completely thrilled about Object::get() and Object::put() doing
special-case stuff for arrays, and we should probably come up with a
better abstraction for it.
But at least it works for now, which is really nice. :^)
This is pretty naive, we just walk up the prototype chain and call any
NativeProperty setter that we find. If we don't find one, we put/set
the value as an own property of the object itself.
Now that Interpreter keeps all arguments in the CallFrame stack, we can
just pass a const-reference to the CallFrame's argument vector to each
function handler (instead of copying it.)
