Allow Qt to wrap long tooltips (fixes #1063)

Implemented without having to touch any translation: by listening for QEvent::ToolTipChange events, then rewriting the tooltips to prefix `<qt/>` if it is not yet rich text.

src/qt/guiutil.h

@@ -2,6 +2,7 @@
 #define GUIUTIL_H
 
 #include <QString>
+#include <QObject>
 
 QT_BEGIN_NAMESPACE
 class QFont;
@@ -69,6 +70,23 @@ namespace GUIUtil
     // Determine whether a widget is hidden behind other windows
     bool isObscured(QWidget *w);
 
+    /** Qt event filter that intercepts ToolTipChange events, and replaces the tooltip with a rich text
+      representation if needed. This assures that Qt can word-wrap long tooltip messages.
+      Tooltips longer than the provided size threshold (in characters) are wrapped.
+     */
+    class ToolTipToRichTextFilter: public QObject
+    {
+        Q_OBJECT
+    public:
+        ToolTipToRichTextFilter(int size_threshold, QObject *parent);
+
+    protected:
+        bool eventFilter(QObject *obj, QEvent *evt);
+
+    private:
+        int size_threshold;
+    };
+
 } // namespace GUIUtil
 
 #endif // GUIUTIL_H