pundit: convert post replacements to pundit.

app/policies/post_replacement_policy.rb

@@ -0,0 +1,19 @@
+class PostReplacementPolicy < ApplicationPolicy
+  def create?
+    user.is_moderator?
+  end
+
+  def update?
+    user.is_moderator?
+  end
+
+  def permitted_attributes_for_create
+    [:replacement_url, :replacement_file, :final_source, :tags]
+  end
+
+  def permitted_attributes_for_update
+    [:file_ext_was, :file_size_was, :image_width_was, :image_height_was,
+     :md5_was, :file_ext, :file_size, :image_width, :image_height, :md5,
+     :original_url, :replacement_url]
+  end
+end