Only disconnect views from the session's bell signal when another view associated with the session is given focus.  This stops an interesting warning where disconnecting one of the view's slots when it lost focus failed because the QEvent::FocusOut event occurred after the TerminalDisplay's destructor had executed, at which point the display widget was, as far as Qt is concerned, just an ordinary QWidget without the slots defined in the TerminalDisplay class.

svn path=/branches/work/konsole-split-view/; revision=646757