Make accidentally activating the link navigation more difficult

Only checking Ctrl and link availability on mouse release was triggering
the navigation too easily.

Now you have to press and release the mouse on the same link, having
Ctrl pressed all the time. In addition, when changing the text selection
the link is also cleared.

Task-number: QTCREATORBUG-134
Reviewed-by: con

src/plugins/texteditor/basetexteditor.h

@@ -538,6 +538,9 @@ protected:
         bool isValid() const
         { return !(pos == -1 || length == -1); }
 
+        bool operator==(const Link &other) const
+        { return pos == other.pos && length == other.length; }
+
         int pos;           // Link position
         int length;        // Link length
 
@@ -593,6 +596,7 @@ private:
 
     QTextBlock collapsedBlockAt(const QPoint &pos, QRect *box = 0) const;
 
+    void updateLink(QMouseEvent *e);
     void showLink(const Link &);
     void clearLink();