[third] Don't move typeahead popups when the body scrolls.

Trac #1479

All our typeaheads use this, but I made it an option that must be enabled
explicitly since it is not default bootstrap behavior.

(imported from commit 97852dc407d1f6dbe46b5fdd2c56d3ed8c6718d2)

static/js/search.js

@@ -52,6 +52,7 @@ exports.initialize = function () {
             search_object = suggestions.lookup_table;
             return suggestions.strings;
         },
+        fixed: true,
         items: 30,
         helpOnEmptyStrings: true,
         naturalSearch: true,