QTimeZone: add member-swap

This is customary for Qt value types these days.

Change-Id: If5374c2595a904337eaef4afc08cdc993229ac25
Reviewed-by: John Layt <jlayt@kde.org>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/corelib/tools/qtimezone.cpp

@@ -422,6 +422,13 @@ QTimeZone &QTimeZone::operator=(const QTimeZone &other)
     return *this;
 }
 
+/*
+    \fn void QTimeZone::swap(QTimeZone &other)
+
+    Swaps this timezone with \a other. This function is very fast and
+    never fails.
+*/
+
 /*!
     \fn QTimeZone &QTimeZone::operator=(QTimeZone &&other)
 

src/corelib/tools/qtimezone.h

@@ -87,9 +87,12 @@ public:
 
     QTimeZone &operator=(const QTimeZone &other);
  #ifdef Q_COMPILER_RVALUE_REFS
-    QTimeZone &operator=(QTimeZone &&other) { std::swap(d, other.d); return *this; }
+    QTimeZone &operator=(QTimeZone &&other) { swap(other); return *this; }
 #endif
 
+    void swap(QTimeZone &other)
+    { d.swap(other.d); }
+
     bool operator==(const QTimeZone &other) const;
     bool operator!=(const QTimeZone &other) const;