Allow to use either :unprocessable_entity or :unprocessable_content

There is just so much code out there referencing the old status
that it's unreasoable to ask Rails users to migrate, especially
since there is 0 gain from the rename.

It's even more problematic because there are many gems and such,
so they all need to be updated to check the Rack version to know
which symbol to emit.

Author: byroot

actionpack/lib/action_controller/metal/redirecting.rb

@@ -249,9 +249,9 @@ def _allow_other_host
 
       def _extract_redirect_to_status(options, response_options)
         if options.is_a?(Hash) && options.key?(:status)
-          Rack::Utils.status_code(options.delete(:status))
+          ActionDispatch::Response.rack_status_code(options.delete(:status))
         elsif response_options.key?(:status)
-          Rack::Utils.status_code(response_options[:status])
+          ActionDispatch::Response.rack_status_code(response_options[:status])
         else
           302
         end

actionpack/lib/action_controller/metal/rendering.rb

@@ -238,7 +238,7 @@ def _normalize_options(options)
         end
 
         if options[:status]
-          options[:status] = Rack::Utils.status_code(options[:status])
+          options[:status] = ActionDispatch::Response.rack_status_code(options[:status])
         end
 
         super

actionpack/lib/action_dispatch/http/response.rb

@@ -46,6 +46,20 @@ class Response
       Headers = ::Rack::Utils::HeaderHash
     end
 
+    class << self
+      if ActionDispatch::Constants::UNPROCESSABLE_CONTENT == :unprocessable_content
+        def rack_status_code(status) # :nodoc:
+          status = :unprocessable_content if status == :unprocessable_entity
+          Rack::Utils.status_code(status)
+        end
+      else
+        def rack_status_code(status) # :nodoc:
+          status = :unprocessable_entity if status == :unprocessable_content
+          Rack::Utils.status_code(status)
+        end
+      end
+    end
+
     # To be deprecated:
     Header = Headers
 
@@ -257,7 +271,7 @@ def sent?;      synchronize { @sent };      end
 
     # Sets the HTTP status code.
     def status=(status)
-      @status = Rack::Utils.status_code(status)
+      @status = Response.rack_status_code(status)
     end
 
     # Sets the HTTP response's content MIME type. For example, in the controller you

actionpack/lib/action_dispatch/middleware/exception_wrapper.rb

@@ -178,7 +178,7 @@ def traces
     end
 
     def self.status_code_for_exception(class_name)
-      Rack::Utils.status_code(@@rescue_responses[class_name])
+      ActionDispatch::Response.rack_status_code(@@rescue_responses[class_name])
     end
 
     def show?(request)

actionpack/lib/action_dispatch/testing/assertion_response.rb

@@ -38,7 +38,7 @@ def code_and_name
 
     private
       def code_from_name(name)
-        GENERIC_RESPONSE_CODES[name] || Rack::Utils.status_code(name)
+        GENERIC_RESPONSE_CODES[name] || ActionDispatch::Response.rack_status_code(name)
       end
 
       def name_from_code(code)