Qt4 - Compile fix for windows.

modules/gui/qt4/playlist_model.cpp

@@ -1073,6 +1073,7 @@ void PLModel::popupSave()
 }
 
 #ifdef WIN32
+#include <shellapi.h>
 void PLModel::popupExplore()
 {
     ShellExecuteW(NULL, L"explore", L"C:\\", NULL, NULL, SW_SHOWNORMAL );

modules/gui/qt4/playlist_model.hpp

@@ -198,6 +198,7 @@ private slots:
     void popupInfo();
     void popupStream();
     void popupSave();
+    void popupExplore();
     void viewchanged( int );
 friend class PLItem;
 };