Debugger: Fix exit crash, dump QVariantList with gdb

Handle QVariantList within dumpers, as gdb does not resolve
typedefs. Disconnect the gdb process on exit, one more round
of event loop when quitting.

src/plugins/debugger/gdb/gdbengine.cpp

@@ -225,7 +225,7 @@ QMainWindow *GdbEngine::mainWindow() const
 GdbEngine::~GdbEngine()
 {
     // prevent sending error messages afterwards
-    disconnect(&m_gdbProc);
+    disconnect(&m_gdbProc, 0, this, 0);
     delete m_gdbAdapter;
     m_gdbAdapter = 0;
 }