Address comments on Gzip implementation

- don't mutate PATH_INFO in env, test
- test fallback content type matches Rack::File
- change assertion style
- make HTTP_ACCEPT_ENCODING comparison case insensitive
- return gzip path from method instead of true/false so we don't have to assume later
- don't allocate un-needed hash.

Original comments:

https://github.com/rails/rails/commit/
cfaaacd9763642e91761de54c90669a88d772e5a#commitcomment-7468728

cc @jeremy

1 files changed, 7 insertions, 0 deletions

diff --git a/guides/source/4_2_release_notes.md b/guides/source/4_2_release_notes.md
index 39655447e3..013e9e8dbe 100644
--- a/guides/source/4_2_release_notes.md
+++ b/guides/source/4_2_release_notes.md
@@ -268,6 +268,13 @@ Please refer to the [Changelog][action-pack] for detailed changes.
 *   Added an option to disable logging of CSRF failures.
     ([Pull Request](https://github.com/rails/rails/pull/14280))
 
+*   When the Rails server is set to serve static assets, gzip assets will now be
+    served if the client supports it and a pre-generated gzip file (.gz) is on disk.
+    By default the asset pipeline generates `.gz` files for all compressible assets.
+    Serving gzip files minimizes data transfer and speeds up asset requests. Always
+    [use a CDN](http://guides.rubyonrails.org/asset_pipeline.html#cdns) if you are
+    serving assets from your Rails server in production.
+    ([Pull Request](https://github.com/rails/rails/pull/16466))
 
 Action View
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