make base_url configurable

lib/rack/url.rb

@@ -6,16 +6,19 @@ module Rewritten
 
     class Url
 
+      attr_accessor :base_url
+
       def initialize(app, &block)
         @app = app
         @translate_backwards = false
         @downcase_before_lookup = false
         @translate_partial = false
+        @base_url = ''
         instance_eval(&block) if block_given?
       end
 
       def is_internal_target?(url)
-        url.nil? or url.start_with?('/') or url.start_with?('http://www.example.org')
+        url.nil? or url.start_with?('/') or url.start_with?(@base_url)
       end
 
       def is_external_target?(url)

test/rack/rewritten_url_test.rb

@@ -65,7 +65,9 @@ def request_url(url, params={})
 
       before {
         @app = MiniTest::Mock.new
-        @rack = Rack::Rewritten::Url.new(@app)
+        @rack = Rack::Rewritten::Url.new(@app) do |config|
+          config.base_url = 'http://www.example.org'
+        end
 
         Rewritten.add_translation '/external/target', 'http://www.external.com'
       }