Raise minimal Qt version to 5.5.1

src/base/torrentfileguard.h

@@ -50,13 +50,9 @@ private:
 
 /// Reads settings for .torrent files from preferences
 /// and sets the file guard up accordingly
-class TorrentFileGuard
+class TorrentFileGuard: private FileGuard
 {
     Q_GADGET
-    // moc from Qt4 ignores Q_ENUMS when it is behind #if QT_VERSION check
-    // this declaration is needed for Qt 4 only
-    // TODO Qt5: remove when dropping Qt4 support
-    Q_ENUMS(AutoDeleteMode)
 
 public:
     TorrentFileGuard(const QString &path = QString());
@@ -79,25 +75,12 @@ public:
 
 private:
     static QMetaEnum modeMetaEnum();
-#if QT_VERSION >= QT_VERSION_CHECK(5, 5, 0)
+
+    TorrentFileGuard(const QString &path, AutoDeleteMode mode);
+
     Q_ENUM(AutoDeleteMode)
-#endif
     AutoDeleteMode m_mode;
     bool m_wasAdded;
-    // Qt 4 moc has troubles with Q_GADGET: if Q_GADGET is present in a class, moc unconditionally
-    // references in the generated code the statiMetaObject from the class ancestor.
-    // Moreover, if the ancestor class has Q_GADGET but does not have other
-    // Q_ declarations, moc does not generate staticMetaObject for it. These results
-    // in referencing the non existent staticMetaObject and such code fails to compile.
-    // This problem is NOT present in Qt 5.7.0 and maybe in some older Qt 5 versions too
-    // Qt 4.8.7 has it.
-    // Therefore, we can't inherit FileGuard :(
-    // TODO Qt5: port to private inheritance when dropping Qt 4 support
-    FileGuard m_guard;
 };
 
-#if QT_VERSION < QT_VERSION_CHECK(5, 5, 0)
-Q_DECLARE_METATYPE(TorrentFileGuard::AutoDeleteMode)
-#endif
-
 #endif // TOFFENTFILEGURAD_H