Tree.java: correctly escape & in default Tooltip

This fixes eclipse-platform/eclipse.platform.ui#1075

When TreeColumn's are too small, a ToolTip is displayed on hover to
reveal the whole Label of an Item (The WIN32-Docs call them 'Inline
ToolTips').
These ToolTips pass through the Composite-ToolTipText-generator which
escapes all & in a Text - allowing to reuse Text from Buttons as
Tooltips. This is a well documented Feature of setToolTipText.
Since TreeItem's Label does not have Mnemonics, we do not assume that the
& needs escaping.

This Commit Escapes all & in default Tooltips that are handled by the
default mechanism.

Author: Maximilian Wittmer

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Tree.java

@@ -5646,7 +5646,7 @@ String toolTipText (NMTTDISPINFO hdr) {
 		if (findCell (pt.x, pt.y, item, index, cellRect, itemRect)) {
 			String text = null;
 			if (index [0] == 0) {
-				text = item [0].text;
+				text = item [0].text.replace("&", "&&");
 			} else {
 				String[] strings = item [0].strings;
 				if (strings != null) text = strings [index [0]];