Avoid extra space in tooltips

When using QTextDocument to check the natutal size of a text, one has
to remove the text margin, which is not useful here.

Fixes bug #11353.

(cherry picked from commit 7db99672e6)

src/frontends/qt4/qt_helpers.cpp

@@ -645,6 +645,7 @@ QString formatToolTip(QString text, int em)
 	QTextDocument td("");
 	td.setHtml(text);
 	td.setDefaultFont(QToolTip::font());
+	td.setDocumentMargin(0);
 	td.setTextWidth(px_width);
 	double best_width = td.idealWidth();
 	// Set the line wrapping with appropriate width

status.23x

@@ -181,6 +181,8 @@ What's new
 
 - Fix display of overset, underset, and stackrel insets (bug 11367).
 
+- Avoid extra space at the end of tooltips (bug 11353).
+
 
 * INTERNALS