fix: GUI Disappearing #1522 (Mac OSX)

- this solution works stable on mac and ensures that the window get's reopened when the user clicks the dock icon .
- tested on 10.8 with Qt4.8.4 and Qt5.0.1

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>

src/qt/bitcoingui.cpp

@@ -155,6 +155,7 @@ BitcoinGUI::~BitcoinGUI()
         trayIcon->hide();
 #ifdef Q_OS_MAC
     delete appMenuBar;
+    MacDockIconHandler::instance()->setMainWindow(NULL);
 #endif
 }
 
@@ -382,6 +383,7 @@ void BitcoinGUI::createTrayIconMenu()
 #else
     // Note: On Mac, the dock icon is used to provide the tray's functionality.
     MacDockIconHandler *dockIconHandler = MacDockIconHandler::instance();
+    dockIconHandler->setMainWindow((QMainWindow *)this);
     trayIconMenu = dockIconHandler->dockMenu();
 #endif