This is an improved fix to the corrupted tab view state bug partially addressed by 0f347be.
Without either fix, NSTabView is converted to a CPTabView where tab view item views are subviews of the NSTabView, while in Cappuccino the selected view item is supposed to be a subview of a CPBox.
Without this fix, CPTabView decoding called addSubview: in initWithCoder: which can cause the superview of a view to become set, only to later be overwritten when the superview ivar is decoded.
This fix removes the tab item view as a subview from the tab view before encoding it in nib2cib, and then makes sure not to call addSubview: while still in the initWithCoder stage, but rather later in awakeFromCib.