Always make notifications with '\n' in bannerText expandable

Right now notifications are expandable if the length of bannerText
exceeds the notification's width - however, if bannerText contains
newlines, it should be expandable regardless of the length.

https://bugzilla.gnome.org/show_bug.cgi?id=610549

js/ui/messageTray.js

@@ -287,7 +287,8 @@ Notification.prototype = {
                 overflow = true;
         }
 
-        if (overflow && this._bannerBodyText)
+        if (this._bannerBodyText &&
+            (overflow || this._bannerBodyText.indexOf('\n') > -1))
             this._addBannerBody();
     },