Support naturalSearch option in typeahead.

The naturalSearch option immediately updates the search box with
the underlying value of a search suggestion when the user moves to
it.

(imported from commit ad5cb5c2591ef4f71a6d648c8839f288cc125cf7)

zephyr/static/third/bootstrap/js/bootstrap.js

@@ -1826,6 +1826,9 @@
     this.source = this.options.source
     this.shown = false
     this.dropup = this.options.dropup
+    // The naturalSearch option causes arrow keys to immediately
+    // update the search box with the underlying values from the
+    // search suggestions.
     this.listen()
   }
 
@@ -1841,6 +1844,11 @@
       return this.hide()
     }
 
+  , set_value: function () {
+      var val = this.$menu.find('.active').data('typeahead-value')
+      this.$element.val(val)
+    }
+
   , select_and_continue: function () {
       // We don't call updater() because it potentially has side-effects.
       // This does mean that smartSpaceBar can't be used in cases where the
@@ -1966,6 +1974,10 @@
       }
 
       next.addClass('active')
+
+      if (this.options.naturalSearch) {
+        this.set_value();
+      }
     }
 
   , prev: function (event) {
@@ -1977,6 +1989,10 @@
       }
 
       prev.addClass('active')
+
+      if (this.options.naturalSearch) {
+        this.set_value();
+      }
     }
 
   , listen: function () {