Use the methods rack provides so we don't have to worry about the exact
header key.

Rack implements the Etag header manipulation methods, so we can use
those instead of ours.

* Introduce `ActionDispatch::Http::Headers#add` to add a value to
  a multivalued header.
* Move `Response#add_header` upstream: https://github.com/rack/rack/pull/957
* Match upstream `Response#have_header?` -> `#has_header?` name change.

YAGNI concurrent-ruby master branch now that 1.0.0.pre3 is released with fixes for warnings and circular require

Bumped version of concurrent-ruby to 1.0.0.pre3, which fixes all
interpreter warnings.

* Move `app/assets/manifest.js` to `app/assets/config/manifest.js`.
  Avoid the suggestion that you can/should deep-link `stylesheets/foo`.
* Pull in all toplevel stylesheets and JavaScripts, not just
  `application.js` and `.css`. Demonstrate how to use `link_directory`
  with a specified `.js`/`.css` type.
* Fix RAILS_ENV handling in assets tests.
* Shush warnings spam from third-party libs that distract from tests.

Since `alias_method_chain` is deprecated we need to use the master version
of the Turbolinks gem as it has support for using `Module#prepend`.

The thread_safe gem is being deprecated and all its code has been merged
into the concurrent-ruby gem. The new class, Concurrent::Map, is exactly
the same as its predecessor except for fixes to two bugs discovered
during the merge.

This will make the Gemfile.lock be dirty in some environments

Ruby 2.2.3 in windows need nokogiri 1.6.7.rc3 as it's the only version having correct pre-compiled so

Known failure on Ruby 2.3/trunk: brianmario/mysql2#671

Just include the modules necessary in the Request object to implement
the things we need.  This should make it easier to build delegate
request objects because the API is smaller

Escaping and unescaping paths is different than query parameters, and we
need to respect that.  This commit uses the new method in Rack to escape
and unescape paths.  Fixes #11816

Fixes https://github.com/rails/rails/commit/4d157ea8c15186c4903fa83f2dc51a5f78d13a37

Without any specification about the version of sprockets-rails, running a
`bundle install` on a brand new app might result in sprockets 0.0.1 being
installed.

However, the minimum requirement is sprockets-rails 2 (see https://github.com/rails/rails/pull/17752/files)

eventually we will refactor this to not know about header hashes

This commit allows us to use one request object rather than allocating
multiple request objects to deal with the session.

duping the request will dup it's underlying env hash.

The latest, currently unreleased, version of queue_classic is required
for this to work. See
https://github.com/QueueClassic/queue_classic/pull/262 for more details.

The concurrent-ruby gem is a toolset containing many concurrency
utilities. Many of these utilities include runtime-specific
optimizations when possible. Rather than clutter the Rails codebase with
concurrency utilities separate from the core task, such tools can be
superseded by similar tools in the more specialized gem. This commit
replaces `ActiveSupport::Concurrency::Latch` with
`Concurrent::CountDownLatch`, which is functionally equivalent.