Left most engine mime type matters

Fixes #478

Author: josh

lib/sprockets/asset_attributes.rb

@@ -83,7 +83,7 @@ def format_content_type
       # `.coffee` files carry an implicit `application/javascript`
       # content type.
       def engine_content_type
-        engine_extensions.reverse.each do |ext|
+        engine_extensions.each do |ext|
           if mime_type = environment.engine_mime_types[ext]
             return mime_type
           end

test/test_asset_attributes.rb

@@ -70,6 +70,11 @@ class TestAssetAttributes < Sprockets::TestCase
       pathname("jquery.tmpl.min.js").content_type
     assert_equal "application/javascript",
       pathname("application.coffee").content_type
+
+    env = Sprockets::Environment.new
+    env.register_engine '.haml', proc {}, mime_type: 'text/html'
+    env.register_engine '.ngt', proc {}, mime_type: 'application/javascript'
+    assert_equal "application/javascript", env.attributes_for("foo.ngt.haml").content_type
   end
 
   private