Fix #5012: Fc2 image link paste not uploading.

Fix referer spoofing not working for certain fc2.com image URLs.

Spoofing the referer like this redirects to an HTML error page:

* curl -H "Referer: http://wwwew.web.fc2.com" http://wwwew.web.fc2.com/e/405.jpg

Spoofing it like this works:

* curl -H "Referer: http://wwwew.web.fc2.com/e/405.jpg" http://wwwew.web.fc2.com/e/405.jpg

app/logical/danbooru/http/spoof_referrer.rb

@@ -6,7 +6,7 @@ module Danbooru
       HTTP::Options.register_feature :spoof_referrer, self
 
       def perform(request, &block)
-        request.headers["Referer"] = request.uri.origin unless request.headers["Referer"].present?
+        request.headers["Referer"] = request.uri unless request.headers["Referer"].present?
         response = yield request
         response
       end

test/functional/uploads_controller_test.rb

@@ -356,6 +356,8 @@ class UploadsControllerTest < ActionDispatch::IntegrationTest
         should_upload_successfully("https://c.fantia.jp/uploads/post/file/1070093/16faf0b1-58d8-4aac-9e86-b243063eaaf1.jpeg")
         should_upload_successfully("https://fantia.jp/posts/1132267")
         should_upload_successfully("https://fantia.jp/products/249638")
+
+        should_upload_successfully("http://wwwew.web.fc2.com/e/405.jpg")
       end
     end
   end