Merge pull request #831 from dhilgarth/feature/fix_post_url

Fix broken post_url with posts with a time in their YAML front matter.

lib/jekyll/tags/post_url.rb

@@ -23,7 +23,7 @@ module Jekyll
         site = context.registers[:site]
 
         site.posts.each do |p|
-          if p == @post
+          if p.slug == @post.slug and p.date.year == @post.date.year and p.date.month == @post.date.month and p.date.day == @post.date.day
             return p.url
           end
         end