New: Allow lazy loading control for combined observer key paths (#2854)
New: Allow lazy loading control for combined observer key paths (#2854)

This pull request adds a kvoValueForKey: method used by _CPKVOForwardingObserver for getting values.
The default action is to just return the valueForKey value.
Override this method if you want any other behavior.
It can be used to just return nil if you are implementing a lazy load behavior on a class.
It can allow a combined binding to observe this object without trigger any lazy loading.
cappuccino/cappuccino,daboe01/cappuccino,daboe01/cappuccino,cappuccino/cappuccino,cappuccino/cappuccino,cappuccino/cappuccino,daboe01/cappuccino,daboe01/cappuccino,daboe01/cappuccino,cappuccino/cappuccino,cappuccino/cappuccino,cappuccino/cappuccino,daboe01/cappuccino,daboe01/cappuccino