xml_http_request fails in IntegrationTests with 3-1-stable

[rubys]

Recent regression in 3-1-stable with Ruby 1.8.7 (works in 3.0.9 with either 1.8.7 or 1.9.2; and works in 3-1-stable with 1.9.2).

Steps to reproduce:

1. Create test/integration/user_stories_test.rb with the following content:

require 'test_helper'
class ProductIntegrationTest < ActionDispatch::IntegrationTest
  test 'xhr' do
    xml_http_request :post, '/products', :id => 1
  end
end

2. Execute the following command:

rake --trace test:integration

expected output (1.9.2)
actual output (1.8.7)

[spastorino]

This is a rack regression I've fixed it here rack/rack#210

[rubys]

I don't believe that this rails issue should be closed until there is a release of rack that fixes the problem.

The current state is: rails 3.0 w/ rack 1.3.1 works; rails 3-1-stable w/ rack 1.3.1 does not.

[spastorino]

@rubys yeah I'm talking with the rack guys about this, anyways doesn't hurt to keep it open just in case :)

[spastorino]

As a reminder this is related #2070 bfolkens@d895104