prevents windows from showing in the taskbar

svn path=/trunk/mcs/; revision=35082

mcs/class/Managed.Windows.Forms/System.Windows.Forms/MenuAPI.cs

@@ -834,7 +834,8 @@ namespace System.Windows.Forms
 		{
 			get {
 				CreateParams cp = base.CreateParams;									
-				cp.Style = unchecked ((int)(WindowStyles.WS_POPUP | WindowStyles.WS_VISIBLE));
+				cp.Style = unchecked ((int)(WindowStyles.WS_POPUP | WindowStyles.WS_VISIBLE));
+				cp.ExStyle |= (int)WindowStyles.WS_EX_TOOLWINDOW;
 				return cp;
 			}
 		}