small bindings fix in CPObjectController

CPObjectController would attempt to remove observations from the new selection in stead of the old selection. This would throw an error when binding to longer compound key paths like selection.customer.name

Fixes #967

AppKit/CPObjectController.j

@@ -503,11 +503,13 @@ var CPObjectControllerObjectClassNameKey                = @"CPObjectControllerOb
 
 @implementation CPControllerSelectionProxy : CPObject
 {
-    id              _controller;
-    id              _keys;
+    id                  _controller;
+    id                  _keys;
 
-    CPDictionary    _cachedValues;
-    CPArray         _observationProxies;
+    CPDictionary        _cachedValues;
+    CPArray             _observationProxies;
+
+    _CPObservableArray  _observedObjects;
 }
 
 - (id)initWithController:(id)aController
@@ -610,7 +612,10 @@ var CPObjectControllerObjectClassNameKey                = @"CPObjectControllerOb
     [proxy setNotifyObject:YES];
     [_observationProxies addObject:proxy];
 
-    [[_controller selectedObjects] addObserver:proxy forKeyPath:aKeyPath options:options context:context];
+    // We keep are reference to the observed objects
+    // because the removeObserver: will be called after the selection changes
+    _observedObjects = [_controller selectedObjects];
+    [_observedObjects addObserver:proxy forKeyPath:aKeyPath options:options context:context];
 }
 
 - (void)removeObserver:(id)anObject forKeyPath:(CPString)aKeyPath
@@ -618,8 +623,10 @@ var CPObjectControllerObjectClassNameKey                = @"CPObjectControllerOb
     var proxy = [[_CPObservationProxy alloc] initWithKeyPath:aKeyPath observer:anObject object:self],
         index = [_observationProxies indexOfObject:proxy];
 
-    [[_controller selectedObjects] removeObserver:[_observationProxies objectAtIndex:index] forKeyPath:aKeyPath];
+    [_observedObjects removeObserver:[_observationProxies objectAtIndex:index] forKeyPath:aKeyPath];
     [_observationProxies removeObjectAtIndex:index];
+
+    _observedObjects = nil;
 }
 
 @end