patch paper_trail to work with RailsAdmin

paper_trail.rb

require "paper_trail/version"

# Make PaperTrail's Version class quack like RailsAdmin's History
class Version

  def username ; whodunnit && User.find(whodunnit).try(:email) || whodunnit ; end
  def message ; "#{event} #{item_type} id #{item_id}" ; end
  def table ; item_type ; end
  def updated_at ; created_at ; end
  # the count(*) that we select in the :number attribute comes back
  # from postgres as a string, so we need to "to_i" it
  def number ; super.to_i ; end
  def month ; super.to_i ; end

  # Make Version look like History when it gets JSON-serialized.
  def as_json(*a)
    {"history" => {"record_count" => number, "month" => month, "year" => year}}.as_json(*a)
  end
end

Beware that this gist asumes (line 6) that you have a user model called User who is been identified by his email address. Your configuration may vary there.