Have Qt poll for shutdown requested, the QT way.

src/qt/bitcoingui.cpp

@@ -24,6 +24,7 @@
 #include "rpcconsole.h"
 #include "ui_interface.h"
 #include "wallet.h"
+#include "init.h"
 
 #ifdef Q_OS_MAC
 #include "macdockiconhandler.h"
@@ -839,3 +840,9 @@ void BitcoinGUI::toggleHidden()
 {
     showNormalIfMinimized(true);
 }
+
+void BitcoinGUI::detectShutdown()
+{
+    if (ShutdownRequested())
+        QMetaObject::invokeMethod(QCoreApplication::instance(), "quit", Qt::QueuedConnection);
+}