Add completion for empty 'defsearch'

vimperator/content/bookmarks.js

@@ -258,7 +258,11 @@ function Bookmarks() //{{{
         "Set the default search engine",
         "string", "google",
         {
-            completer: function completer(context) completion.search(context, true),
+            completer: function completer(context)
+            {
+                completion.search(context, true)
+                context.completions = [["", "Don't perform searches by default"]].concat(context.completions);
+            },
             validator: Option.validateCompleter
         });