Update Vendored Rack to 1.2.0

Also update tests for itextomml 1.3.25.

vendor/plugins/rack/spec/spec_config.rb

@@ -0,0 +1,23 @@
+require 'rack/builder'
+require 'rack/config'
+require 'rack/content_length'
+require 'rack/lint'
+require 'rack/mock'
+
+describe Rack::Config do
+  should "accept a block that modifies the environment" do
+    app = Rack::Builder.new do
+      use Rack::Lint
+      use Rack::ContentLength
+      use Rack::Config do |env|
+        env['greeting'] = 'hello'
+      end
+      run lambda { |env|
+        [200, {'Content-Type' => 'text/plain'}, [env['greeting'] || '']]
+      }
+    end
+
+    response = Rack::MockRequest.new(app).get('/')
+    response.body.should.equal('hello')
+  end
+end