Avoid automatically fetching the vendor/sizzle git submodule.

Rakefile

@@ -13,6 +13,7 @@ module PrototypeHelper
   TEST_UNIT_DIR = File.join(TEST_DIR, 'unit')
   TMP_DIR       = File.join(TEST_UNIT_DIR, 'tmp')
   VERSION       = YAML.load(IO.read(File.join(SRC_DIR, 'constants.yml')))['PROTOTYPE_VERSION']
+  DEFAULT_SELECTOR_ENGINE = 'sizzle'
 
   %w[sprockets pdoc unittest_js caja_builder].each do |name|
     $:.unshift File.join(PrototypeHelper::ROOT_DIR, 'vendor', name, 'lib')
@@ -45,8 +46,8 @@ module PrototypeHelper
     require_sprockets
     load_path = [SRC_DIR]
     
-    if selector = options[:selector_engine]
-      load_path << get_selector_engine(selector)
+    if selector_path = get_selector_engine(options[:selector_engine])
+      load_path << selector_path
     end
     
     secretary = Sprockets::Secretary.new(
@@ -66,7 +67,7 @@ module PrototypeHelper
       :path => 'src',
       :source => file,
       :destination => temp_path,
-      :selector_engine => ENV['SELECTOR_ENGINE'] || 'sizzle',
+      :selector_engine => ENV['SELECTOR_ENGINE'] || DEFAULT_SELECTOR_ENGINE,
       :strip_comments => false
     )
     rm_rf DOC_DIR
@@ -99,8 +100,7 @@ module PrototypeHelper
   def self.get_selector_engine(name)
     submodule_path = File.join(ROOT_DIR, "vendor", name)
     return submodule_path if File.exist?(File.join(submodule_path, "repository", ".git"))
-    ext_path = File.join(ROOT_DIR, "ext", name)
-    return ext_path if File.exist?(ext_path)
+    return if name == DEFAULT_SELECTOR_ENGINE
     
     get_submodule('the required selector engine', "#{name}/repository")
     unless File.exist?(submodule_path)
@@ -151,7 +151,7 @@ task :dist do
   PrototypeHelper.sprocketize(
     :path => 'src',
     :source => 'prototype.js',
-    :selector_engine => ENV['SELECTOR_ENGINE'] || 'sizzle'
+    :selector_engine => ENV['SELECTOR_ENGINE'] || PrototypeHelper::DEFAULT_SELECTOR_ENGINE
   )
 end