Bugfix: Fix various places where Bitcoin-Qt was being shutdown improperly

(Partial/merge of upstream 9247134eab, 1a3f0da922, and 3e34352222)

src/init.cpp

@@ -41,6 +41,17 @@ void ExitTimeout(void* parg)
 #endif
 }
 
+void StartShutdown()
+{
+#ifdef QT_GUI
+    // ensure we leave the Qt main loop for a clean GUI exit (Shutdown() is called in bitcoin.cpp afterwards)
+    QueueShutdown();
+#else
+    // Without UI, Shutdown() can simply be started in a new thread
+    CreateThread(Shutdown, NULL);
+#endif
+}
+
 void Shutdown(void* parg)
 {
     static CCriticalSection cs_Shutdown;