This can make make included javascripts/stylesheets from expansions t…

…o be duplicated

or grow forever if you call register_*_expansion more than once

Fix a Regression introduced here 55b13c5

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -376,8 +376,7 @@ def javascript_include_tag(*sources)
       #     <script type="text/javascript" src="/javascripts/tail.js"></script>
       def self.register_javascript_expansion(expansions)
         expansions.each do |key, values|
-          @@javascript_expansions[key] ||= []
-          @@javascript_expansions[key] += Array(values)
+          @@javascript_expansions[key] = (@@javascript_expansions[key] || []) | Array(values)
         end
       end
 
@@ -394,8 +393,7 @@ def self.register_javascript_expansion(expansions)
       #     <link href="/stylesheets/tail.css"  media="screen" rel="stylesheet" type="text/css" />
       def self.register_stylesheet_expansion(expansions)
         expansions.each do |key, values|
-          @@stylesheet_expansions[key] ||= []
-          @@stylesheet_expansions[key] += Array(values)
+          @@stylesheet_expansions[key] = (@@stylesheet_expansions[key] || []) | Array(values)
         end
       end
 

actionpack/test/template/asset_tag_helper_test.rb

@@ -278,6 +278,7 @@ def test_registering_javascript_expansions_merges_with_existing_expansions
     ENV["RAILS_ASSET_ID"] = ""
     ActionView::Helpers::AssetTagHelper::register_javascript_expansion :can_merge => ['bank']
     ActionView::Helpers::AssetTagHelper::register_javascript_expansion :can_merge => ['robber']
+    ActionView::Helpers::AssetTagHelper::register_javascript_expansion :can_merge => ['bank']
     assert_dom_equal  %(<script src="/javascripts/bank.js" type="text/javascript"></script>\n<script src="/javascripts/robber.js" type="text/javascript"></script>), javascript_include_tag(:can_merge)
   end
 
@@ -351,6 +352,7 @@ def test_registering_stylesheet_expansions_merges_with_existing_expansions
     ENV["RAILS_ASSET_ID"] = ""
     ActionView::Helpers::AssetTagHelper::register_stylesheet_expansion :can_merge => ['bank']
     ActionView::Helpers::AssetTagHelper::register_stylesheet_expansion :can_merge => ['robber']
+    ActionView::Helpers::AssetTagHelper::register_stylesheet_expansion :can_merge => ['bank']
     assert_dom_equal  %(<link href="/stylesheets/bank.css" media="screen" rel="stylesheet" type="text/css" />\n<link href="/stylesheets/robber.css" media="screen" rel="stylesheet" type="text/css" />), stylesheet_link_tag(:can_merge)
   end