[Mono-osx] [MonoMac] KVC, KVO api cleanup

[kjpou]

Miguel

Concerning the following methods:

        ObserveValue
        AddObserver
        RemoveObserver
        WillChangeValue
        DidChangeValue
        WillChange
        DidChange
        WillChange
        DidChange
        GetKeyPathsForValuesAffecting
        AutomaticallyNotifiesObserversForKey
        ValueForKey
        SetValueForKey
        ValueForKeyPath
        SetValueForKeyPath
        ValueForUndefinedKey
        SetValueForUndefinedKey
        SetNilValueForKey

Right now the key and keyPath are NSStrings.  Can we move them to type 
strings?

That will clean up the programs, keep casting down to a minimum and 
bring them into line with the Binding methods that already use string 
instead of NSString.

I can have a patch for you in just a little while.

Kenneth