Determines whether the pane can be closed.
The framework calls this method to determine whether the pane can be closed. If the method returns TRUE, a Close button is added to the pane's title bar or, if the pane is floating, to the title bar of the pane's miniframe window.
During construction, you can set this ability by passing the AFX_CBRS_CLOSE flag to CBasePane::CreateEx.
The default implementation checks for the AFX_CBRS_CLOSE flag.