Use mongrel instead of thin so we can run more than one server at once

fake_braintree.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'i18n'
   s.add_dependency 'sinatra'
   s.add_dependency 'braintree', '~> 2.5'
-  s.add_dependency 'thin'
+  s.add_dependency 'mongrel', '~> 1.2.0.pre'
 
   s.add_development_dependency 'rspec', '~> 2.6.0'
   s.add_development_dependency 'mocha', '~> 0.9.12'

lib/fake_braintree.rb

@@ -2,6 +2,7 @@
 require 'braintree'
 require 'capybara'
 require 'capybara/server'
+require 'rack/handler/mongrel'
 
 require 'fake_braintree/helpers'
 require 'fake_braintree/customer'
@@ -108,9 +109,21 @@ def self.set_configuration
   end
 
   def self.boot_server
-    server = Capybara::Server.new(FakeBraintree::SinatraApp)
-    server.boot
-    ENV['GATEWAY_PORT'] = server.port.to_s
+    with_mongrel_runner do
+      server = Capybara::Server.new(FakeBraintree::SinatraApp)
+      server.boot
+      ENV['GATEWAY_PORT'] = server.port.to_s
+    end
+  end
+
+  def self.with_mongrel_runner
+    default_server_process = Capybara.server
+    Capybara.server do |app, port|
+      Rack::Handler::Mongrel.run(app, :Port => port)
+    end
+    yield
+  ensure
+    Capybara.server(&default_server_process)
   end
 end