Don't load mail gem until it's really needed

Implementing ruby autoload on big ugly mikel/mail gem:
huge improvement (around 20%) of padrino framework load speed

padrino-mailer/lib/padrino-mailer.rb

@@ -5,10 +5,9 @@
   require 'sinatra/tilt'
 end
 require 'padrino-core/support_lite' unless defined?(SupportLite)
-require 'mail'
+autoload :Mail, 'mail'
 
 # Require respecting order of our dependencies
-FileSet.glob_require('padrino-mailer/**/*.rb', __FILE__)
 
 module Padrino
   ##
@@ -45,6 +44,10 @@ class << self
       #
       # @api public
       def registered(app)
+        require 'padrino-mailer/base'
+        autoload :Mail, 'padrino-mailer/ext'
+        require 'padrino-mailer/helpers'
+        require 'padrino-mailer/mime'
         app.helpers Padrino::Mailer::Helpers
       end
       alias :included :registered