ActionMailer plain text layout fix

actionmailer_layout_patch.rb

# Patch Rails so that a plain text mailer view won't be rendered with the layout
# Only tested in Rails 2.2 - I'm not sure how this works with 2.3
module ActionMailer
  class Base  
    def candidate_for_layout?(options)
      return false if ActionView::Template === options[:file] && options[:file].content_type == "text/plain"
      !@template.send(:_exempt_from_layout?, default_template_name)
    end
  end
end