code gardening in ActionController::Renderers

* Renames _handle_render_options to _render_to_body_with_renderer, which is more
  intention-revealing.

* The name of the dynamically generated method for a renderer with key :js was
  "_render_option_js".

  That name is too weak. :js is an option if you see the render argument as just
  a generic options hash, but in the context of renderers that's the renderer
  key, is what identifies the renderer.

  Now "_render_with_renderer_js" is generated instead, which is crystal clear.

* The name of the dynamically generated method for the renderer was constructed
  using string literals in a few places. That is now encapsulated in a method.

* Since we were on it, also removed a couple of redundant selfs.

actionpack/lib/action_controller/metal/renderers.rb

@@ -34,14 +34,15 @@ module ActionController
     end
 
     def render_to_body(options)
-      _handle_render_options(options) || super
+      _render_to_body_with_renderer(options) || super
     end
 
-    def _handle_render_options(options)
+    def _render_to_body_with_renderer(options)
       _renderers.each do |name|
         if options.key?(name)
           _process_options(options)
-          return send("_render_option_#{name}", options.delete(name), options)
+          method_name = Renderers._render_with_renderer_method_name(name)
+          return send(method_name, options.delete(name), options)
         end
       end
       nil
@@ -51,6 +52,10 @@ module ActionController
     # Default values are <tt>:json</tt>, <tt>:js</tt>, <tt>:xml</tt>.
     RENDERERS = Set.new
 
+    def self._render_with_renderer_method_name(key)
+      "_render_with_renderer_#{key}"
+    end
+
     # Adds a new renderer to call within controller actions.
     # A renderer is invoked by passing its name as an option to
     # <tt>AbstractController::Rendering#render</tt>. To create a renderer
@@ -84,7 +89,7 @@ module ActionController
     # <tt>ActionController::MimeResponds::ClassMethods.respond_to</tt> and
     # <tt>ActionController::MimeResponds#respond_with</tt>
     def self.add(key, &block)
-      define_method("_render_option_#{key}", &block)
+      define_method(_render_with_renderer_method_name(key), &block)
       RENDERERS << key.to_sym
     end
 
@@ -95,8 +100,8 @@ module ActionController
     #   ActionController::Renderers.remove(:csv)
     def self.remove(key)
       RENDERERS.delete(key.to_sym)
-      method = "_render_option_#{key}"
-      remove_method(method) if method_defined?(method)
+      method_name = _render_with_renderer_method_name(key)
+      remove_method(method_name) if method_defined?(method_name)
     end
 
     module All
@@ -112,7 +117,7 @@ module ActionController
       json = json.to_json(options) unless json.kind_of?(String)
 
       if options[:callback].present?
-        if self.content_type.nil? || self.content_type == Mime::JSON
+        if content_type.nil? || content_type == Mime::JSON
           self.content_type = Mime::JS
         end