Fix find_focusable_child to use lowercase when comparing with focusable widgets

src/common.js

@@ -3177,12 +3177,10 @@
         if (!element.is(':visible')) {
             return null;
         }
-        if (~['input', 'select', 'textarea'].indexOf(element[0].tagName)) {
+        if (~['input', 'select', 'textarea'].indexOf(
+                    element[0].tagName.toLowerCase())) {
             return element;
         }
-        if (element.children()) {
-            return null;
-        }
 
         children = Sao.common.get_focus_chain(element);
         for (i = 0, len = children.length; i < len; i++) {