Only require builder at startup if we need to monkey with its String#to_xs demands

activesupport/lib/active_support/core_ext/string/xchar.rb

 begin
-  # See http://bogomips.org/fast_xs/ by Eric Wong
+  # See http://bogomips.org/fast_xs/ by Eric Wong.
+  # Also included with hpricot.
   require 'fast_xs'
+rescue LoadError
+  # fast_xs extension unavailable
+else
+  begin
+    require 'builder'
+  rescue LoadError
+    # builder demands the first shot at defining String#to_xs
+  end
 
   class String
     alias_method :original_xs, :to_xs if method_defined?(:to_xs)
     alias_method :to_xs, :fast_xs
   end
-rescue LoadError
-  # fast_xs extension unavailable.
 end

activesupport/lib/active_support/vendor.rb

@@ -6,7 +6,6 @@
 rescue Gem::LoadError
   $:.unshift "#{File.dirname(__FILE__)}/vendor/builder-2.1.2"
 end
-require 'builder'
 
 begin
   gem 'memcache-client', '>= 1.6.5'

activesupport/test/core_ext/hash_ext_test.rb

 require 'abstract_unit'
-require 'builder'
 
 class HashExtTest < Test::Unit::TestCase
   def setup