More fixes to the Lazy Data Source!

• Invocation of -noteChangedChildren has been changed from -objectWillChangeNote to new custom setters -[Stark setParent:] and -[Stark setIndex:], so I could do it *after* the change rather than before.
• Added method -[ContentOutlineView checkAllProxies:]
• -[ContentOutlineView showItems:selectThem:expandAsNeeded:] now properly handles proxies vs. starks.
• Added method -cleanObject: to NSMutableArray (SSYDisjoint).