Fix for issue #777, also fixed a declared type while I was at it

AppKit/CPMenu/CPMenu.j

@@ -75,7 +75,7 @@ var _CPMenuBarVisible               = NO,
 
     id              _delegate;
 
-    CPMenuItem      _highlightedIndex;
+    int             _highlightedIndex;
     _CPMenuWindow   _menuWindow;
 }
 

AppKit/CPPopUpButton.j

@@ -662,6 +662,9 @@ CPPopUpButtonStatePullsDown = CPThemeState("pulls-down");
             location = CGPointMake(CGRectGetMinX(contentRect) - standardLeftMargin, 0.0);
 
         minimumWidth += standardLeftMargin;
+        
+        // To ensure the selected item is highlighted correctly, unset the highlighted item
+        [menu _highlightItemAtIndex:CPNotFound];
     }
 
     [menu setMinimumWidth:minimumWidth];