sort posts before rendering so next and previous posts work

Signed-off-by: Nick Quaranto <nick@quaran.to>

lib/jekyll/site.rb

@@ -130,12 +130,13 @@ module Jekyll
         end
       end
 
+      self.posts.sort!
+
       # second pass renders each post now that full site payload is available
       self.posts.each do |post|
         post.render(self.layouts, site_payload)
       end
 
-      self.posts.sort!
       self.categories.values.map { |cats| cats.sort! { |a, b| b <=> a} }
     rescue Errno::ENOENT => e
       # ignore missing layout dir