Merge pull request #605 from pvdb/loaded_features_builtin

refactor: use `$LOADED_FEATURES` built-in instead of `$"`

lib/rake/application.rb

@@ -691,7 +691,7 @@ def handle_options(argv) # :nodoc:
 
     # Similar to the regular Ruby +require+ command, but will check
     # for *.rake files in addition to *.rb files.
-    def rake_require(file_name, paths=$LOAD_PATH, loaded=$") # :nodoc:
+    def rake_require(file_name, paths=$LOAD_PATH, loaded=$LOADED_FEATURES) # :nodoc:
       fn = file_name + ".rake"
       return false if loaded.include?(fn)
       paths.each do |path|