Set focus to *filename* if this file has been opened.

        Return the editor instance associated to *filename*.

def set_current_filename(self, filename, editorwindow=None, focus=True):
        """Set focus to *filename* if this file has been opened.

        Return the editor instance associated to *filename*.
        """
        editorstack = self.get_current_editorstack(editorwindow)
        return editorstack.set_current_filename(filename, focus)