Fixed casso variables not created in some circumstances. Better handling of mixed constrained/not constrained trees. Fixed hugging/compression nib2cib decoding. Fixed CPLayoutAttributeBaseline (=centerY for now). CPLayoutConstraintCibTest shows a CPAlert-like layout with buttons.
Allow custom layout if subviews are not involved in any constraint. This is temporary, we need a cleaner way to mix views with constraints / autosizing / custom layout.