enumerable.
* ext/psych/lib/psych/visitors/depth_first.rb: Add a depth-first
visitor to enumerate over a YAML AST in a depth-first fashion
* test/psych/nodes/test_enumerable.rb: test for enumerating nodes
* test/psych/visitors/test_depth_first.rb: test for depth-first
visitor
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30624 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
