Fixed: CPComboBox don't close when clicking on the scroll

Previously CPComboBox don't close when clicking on the scroll, now it does

Fixed #1991
Fixed: The delegate method shouldSelectItem doesn't work in CPOutlineView

Previously the delegate method shouldSelectItem didn't work in CPOutlineView.
It didn't work because the checking method _delegateRespondsToSelectionIndexesForProposedSelection and _delegateRespondsToShouldSelectRow didn't check if the real delegate of the outlineView implemented the methods
Changed comment
Merge pull request #2006 from Dogild/outlineView-selectItem

Fixed: The delegate method shouldSelectItem doesn't work in CPOutlineView
Merge pull request #2004 from Dogild/comboBox-trapMouse

Fixed: CPComboBox don't close when clicking on the scroll
Merge branch 'master' of https://github.com/cappuccino/cappuccino