Fix #3642: Issues with sequential pagination.

As of Rails 5, overriding `to_a` on an ActiveRecord collection does
nothing. We need to override `records` instead.

ref: cdd45fa09d

app/logical/danbooru/paginator/sequential_collection_extension.rb

@@ -19,7 +19,10 @@ module Danbooru
         end
       end
 
-      def to_a
+      # XXX Hack: in sequential pagination we fetch one more record than we need
+      # so that we can tell when we're on the first or last page. Here we override
+      # a rails internal method to discard that extra record. See #2044, #3642.
+      def records
         if sequential_paginator_mode == :before
           super.first(records_per_page)
         else