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.
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.
