MDL-21235 input select improved BC

lib/outputcomponents.php

@@ -447,6 +447,10 @@ class html_writer {
                 }
             }
             $options = $nothing + $options; // keep keys, do not override
+
+        } else if (is_string($nothing) and $nothing !== '') {
+            // BC
+            $options = array(''=>$nothing) + $options;
         } 
 
         // we may accept more values if multiple attribute specified