made the signals of PluginConnection interface pure virtual

BasePlugin/PluginConnectionInterface.hh

@@ -86,7 +86,7 @@ class PluginConnectionInterface {
      * _slot is the slot name. Use it like with regular connect ( <tt>SLOT(...)</tt> ) macro
      *
      */
-     virtual void crossPluginConnect( QString /*_pluginName1*/, const char* /*_signal*/, QString /*_pluginName2*/, const char* /*_slot*/) {};
+     virtual void crossPluginConnect( QString /*_pluginName1*/, const char* /*_signal*/, QString /*_pluginName2*/, const char* /*_slot*/) = 0;
 
      /** \brief connect signals and slots of plugins across plugins using Qt::QueuedConnection
      *
@@ -97,7 +97,7 @@ class PluginConnectionInterface {
      * _slot is the slot name. Use it like with regular connect ( <tt>SLOT(...)</tt> ) macro
      *
      */
-     virtual void crossPluginConnectQueued( QString /*_pluginName1*/, const char* /*_signal*/, QString /*_pluginName2*/, const char* /*_slot*/) {};
+     virtual void crossPluginConnectQueued( QString /*_pluginName1*/, const char* /*_signal*/, QString /*_pluginName2*/, const char* /*_slot*/) = 0;
 
 
    public :