from YAML files. * ext/psych/lib/psych/visitors/yaml_tree.rb: Hash subclasses can be dumped to YAML files. * test/psych/test_hash.rb: corresponding test. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@31961 b2dd03c8-39d4-4d8f-98ff-823fe69b080e