Add wxAuiManager::AlwaysUsesLiveResize()

This allows to check if it's worth specifying wxAUI_MGR_LIVE_RESIZE or
not and allows to get rid of the corresponding menu item in the sample
if it doesn't do anything anyhow.

include/wx/aui/framemanager.h

@@ -412,6 +412,8 @@ public:
 
     void SetFlags(unsigned int flags);
     unsigned int GetFlags() const;
+
+    static bool AlwaysUsesLiveResize();
     bool HasLiveResize() const;
 
     void SetManagedWindow(wxWindow* managedWnd);