gistfile1.rb

Preference-ENGINE:/Users/tomohiro:(---) 2.0.0-rc2
2:16:> irb
irb(main):001:0> require 'fiddle'
=> true
irb(main):002:0> DL
NameError: uninitialized constant DL
  from (irb):2
	from /Users/tomohiro/.rbenv/versions/2.0.0-rc2/bin/irb:12:in `<main>'
irb(main):003:0> 

gistfile2.rb

Preference-ENGINE:/Users/tomohiro:(---) 2.0.0-rc2
2:18:> irb
irb(main):001:0> require 'dl'
DL is deprecated, please use Fiddle
=> true
irb(main):002:0> DL
=> DL
irb(main):003:0> DL.fiddle?
=> true
irb(main):004:0> 

gistfile3.rb

Preference-ENGINE:/Users/tomohiro:(---) 1.9.3-p374
2:18:> irb
irb(main):001:0> require 'fiddle'
=> true
irb(main):002:0> DL
=> DL
irb(main):003:0> DL.fiddle?
=> true
irb(main):004:0> 

@tenderlove Thank you for your information!
and thank you for your patch for spring!

done: rails/spring#51