begin transitioning builders to using instance variables instead of #run options Hash fields

build_tests/json_to_yaml/Rsconscript

@@ -3,15 +3,14 @@ build do
     require 'json'
     require 'yaml'
     env.add_builder(:JsonToYaml) do |params|
-      target, sources, cache, env, vars = params.values_at(:target, :sources, :cache, :env, :vars)
-      unless cache.up_to_date?(target, :JsonToYaml, sources, env)
-        cache.mkdir_p(File.dirname(target))
-        File.open(target, 'w') do |f|
-          f.write(YAML.dump(JSON.load(IO.read(sources.first))))
+      unless @cache.up_to_date?(@target, :JsonToYaml, @sources, @env)
+        @cache.mkdir_p(File.dirname(@target))
+        File.open(@target, 'w') do |f|
+          f.write(YAML.dump(JSON.load(IO.read(@sources.first))))
         end
-        cache.register_build(target, :JsonToYaml, sources, env)
+        @cache.register_build(@target, :JsonToYaml, @sources, @env)
       end
-      target
+      @target
     end
     env.JsonToYaml('foo.yml', 'foo.json')
   end