fix truly stupid markdown error

lib/middleman/core_extensions/front_matter.rb

@@ -8,7 +8,7 @@ module Middleman::CoreExtensions::FrontMatter
       
       ::Tilt::register RDiscountTemplate, 'markdown', 'mkd', 'md'
       ::Tilt::register RedcarpetTemplate, 'markdown', 'mkd', 'md'
-      ::Tilt.prefer(RDiscountTemplate)
+      app.set :markdown_engine, RDiscountTemplate
       
       ::Tilt::register RedClothTemplate,  'textile'
       ::Tilt.prefer(RedClothTemplate)

lib/middleman/renderers/markdown.rb

@@ -1,9 +1,9 @@
 module Middleman::Renderers::Markdown
   class << self
     def registered(app)
-      app.set :markdown, ::Tilt::RDiscountTemplate
+      app.set :markdown_engine, ::Tilt::RDiscountTemplate
       app.after_feature_init do
-        ::Tilt.prefer(app.settings.markdown)
+        ::Tilt.prefer(app.settings.markdown_engine)
       end
     end
     alias :included :registered

lib/middleman/version.rb

@@ -1,3 +1,3 @@
 module Middleman
-  VERSION = "2.0.0.rc2"
+  VERSION = "2.0.0.rc3"
 end