Add clear() to QPointer for QWeakPointer compatibility.

Change-Id: I9efc162bf56775c7ebcff4e3b79a997edc4ceaeb
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qpointer.cpp

@@ -170,6 +170,14 @@
     there is no referenced object; otherwise returns false.
 */
 
+/*!
+    \fn void QPointer::clear()
+
+    Clears this QPointer object.
+
+    \sa isNull()
+*/
+
 /*!
     \fn T* QPointer::operator->() const
 

src/corelib/kernel/qpointer.h

@@ -69,6 +69,9 @@ protected:
 
     inline bool isNull() const
     { return wp.isNull(); }
+
+    inline void clear()
+    { wp.clear(); }
 };
 
 template <class T>
@@ -93,8 +96,10 @@ public:
     { return data(); }
 #ifdef qdoc
     inline bool isNull() const;
+    inline void clear() const;
 #else
     using QPointerBase::isNull;
+    using QPointerBase::clear;
 #endif
 };
 template <class T> Q_DECLARE_TYPEINFO_BODY(QPointer<T>, Q_MOVABLE_TYPE);