Fix compilation.

src/core/feeddownloader.cpp

@@ -23,6 +23,7 @@
 #include <QThread>
 #include <QDebug>
 #include <QMetaType>
+#include <QMutex>
 #include <QThreadPool>
 
 

src/core/feeddownloader.h

@@ -49,6 +49,8 @@ class FeedDownloadResults {
     QList<QPair<QString,int> > m_updatedFeeds;
 };
 
+class QMutex;
+
 // This class offers means to "update" feeds and "special" categories.
 // NOTE: This class is used within separate thread.
 class FeedDownloader : public QObject {