Ensure that loading metals from the main app and engines works on older Ruby...

Ensure that loading metals from the main app and engines works on older Ruby versions [#2143 state:resolved]
Signed-off-by: NJoshua Peek <josh@joshpeek.com>

railties/lib/rails/rack/metal.rb

@@ -15,9 +15,11 @@ def self.metals
         metal_glob = metal_paths.map{ |base| "#{base}/**/*.rb" }
         all_metals = {}
 
-        Dir[*metal_glob].sort.map do |file|
-          file = file.match(matcher)[1]
-          all_metals[file.classify] = file
+        metal_glob.each do |glob|
+          Dir[glob].sort.map do |file|
+            file = file.match(matcher)[1]
+            all_metals[file.classify] = file
+          end
         end
 
         load_list = requested_metals || all_metals.keys

railties/test/metal_test.rb

@@ -41,6 +41,15 @@ def test_metal_finding_with_requested_metals_should_work_with_subfolders
     end
   end
 
+  def test_metal_finding_should_work_with_multiple_metal_paths_in_185_and_below
+    use_appdir("singlemetal") do
+      engine_metal_path = "#{File.dirname(__FILE__)}/fixtures/plugins/engines/engine/app/metal" 
+      Rails::Rack::Metal.metal_paths << engine_metal_path
+      $LOAD_PATH << engine_metal_path
+      assert_equal(["FooMetal", "EngineMetal"], found_metals_as_string_array)
+    end
+  end
+
   private
 
   def use_appdir(root)