Ruby

• ext/fiddle/*: Adding fiddle library to wrap libffi
• test/fiddle/*: testing fiddle extension
• ext/dl/lib/dl.rb: Requiring fiddle if it is available
• ext/dl/lib/dl/callback.rb: using Fiddle if it is available
• ext/dl/lib/dl/func.rb: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27640 b2dd03c8-39d4-4d8f-98ff-823fe69b080e