Check whether there is already an instance of the gosty app around

modules/gui/src/gosty_app.cc

@@ -66,6 +66,10 @@ GostyApp* GostyApp::Instance() {
   return GostyApp::app_;
 }
 
+bool GostyApp::ValidInstance() {
+  return GostyApp::app_ != NULL;
+}
+
 void GostyApp::SetAppTitle(const QString& app_title)
 {
   main_->setWindowTitle(app_title);

modules/gui/src/gosty_app.hh

@@ -157,6 +157,11 @@ public:
   /// \return the GostyApp instance
   static GostyApp* Instance();
 
+  /// \brief 
+  /// GostyApp is implemented as Singleton. This returns whether there is 
+  /// already a valid instance around
+  static bool ValidInstance();
+
   /// \brief This methods sets the Title of this Application
   /// \param app_title Title that will be displayed in the title bar
   void SetAppTitle(const QString& app_title);