Make wxSTAY_ON_TOP and other window styles toggleable via SetWindowStyleFlag under OS X Cocoa.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62568 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/nonownedwnd.h

@@ -80,6 +80,7 @@ public:
     static void MacDelayedDeactivation(long timestamp);
     virtual void MacActivate( long timestamp , bool inIsActivating ) ;
 
+    virtual void SetWindowStyleFlag(long flags);
 
     virtual void Raise();
     virtual void Lower();