add hide_results_on_select option (#2687)

hide_results_on_select will default to true, to keep it backwards
compatible.

fixes #1546

coffee/chosen.jquery.coffee

@@ -360,7 +360,7 @@ class Chosen extends AbstractChosen
       else
         this.single_set_selected_text(this.choice_label(item))
 
-      this.results_hide() unless (evt.metaKey or evt.ctrlKey) and @is_multiple
+      this.results_hide() unless @is_multiple && (!@hide_results_on_select || (evt.metaKey or evt.ctrlKey))
       this.show_search_field_default()
 
       @form_field_jq.trigger "change", {'selected': @form_field.options[item.options_index].value} if @is_multiple || @form_field.selectedIndex != @current_selectedIndex

coffee/chosen.proto.coffee

@@ -351,7 +351,7 @@ class @Chosen extends AbstractChosen
       else
         this.single_set_selected_text(this.choice_label(item))
 
-      this.results_hide() unless (evt.metaKey or evt.ctrlKey) and @is_multiple
+      this.results_hide() unless @is_multiple && (!@hide_results_on_select || (evt.metaKey or evt.ctrlKey))
       this.show_search_field_default()
 
       @form_field.simulate("change") if typeof Event.simulate is 'function' && (@is_multiple || @form_field.selectedIndex != @current_selectedIndex)

coffee/lib/abstract-chosen.coffee

@@ -34,6 +34,7 @@ class AbstractChosen
     @include_group_label_in_selected = @options.include_group_label_in_selected || false
     @max_shown_results = @options.max_shown_results || Number.POSITIVE_INFINITY
     @case_sensitive_search = @options.case_sensitive_search || false
+    @hide_results_on_select = if @options.hide_results_on_select? then @options.hide_results_on_select else true
 
   set_default_text: ->
     if @form_field.getAttribute("data-placeholder")

public/options.html

@@ -130,6 +130,13 @@ <h3>Example:</h3>
             <p>By default Chosen's search is case-insensitive. Setting this option to <code class="language-javascript">true</code> makes the search case-sensitive.</p>
           </td>
         </tr>
+        <tr>
+          <td>hide_results_on_select</td>
+          <td>true</td>
+          <td>
+            <p>By default Chosen's results are hidden after a option is selected. Setting this option to <code class="language-javascript">false</code> will keep the results open after selection. This only applies to multiple selects.</p>
+          </td>
+        </tr>
       </table>
 
       <h2><a name="attributes" class="anchor" href="#attributes">Attributes</a></h2>