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.cpp

@@ -214,5 +214,29 @@ bool isObscured(QWidget *w)
            && checkPoint(QPoint(w->width()/2, w->height()/2), w));
 }
 
+ToolTipToRichTextFilter::ToolTipToRichTextFilter(int size_threshold, QObject *parent):
+    size_threshold(size_threshold), QObject(parent)
+{
+
+}
+
+bool ToolTipToRichTextFilter::eventFilter(QObject *obj, QEvent *evt)
+{
+    if(evt->type() == QEvent::ToolTipChange)
+    {
+        QWidget *widget = static_cast<QWidget*>(obj);
+        QString tooltip = widget->toolTip();
+        if(!Qt::mightBeRichText(tooltip) && tooltip.size() > size_threshold)
+        {
+            // Prefix <qt/> to make sure Qt detects this as rich text
+            // Escape the current message as HTML and replace \n by <br>
+            tooltip = "<qt/>" + HtmlEscape(tooltip, true);
+            widget->setToolTip(tooltip);
+            return true;
+        }
+    }
+    return QObject::eventFilter(obj, evt);
+}
+
 } // namespace GUIUtil