* ext/psych/lib/psych/visitors/yaml_tree.rb: change output reference
  ids to be sequential numbers.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39143 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* ext/psych/lib/psych/visitors/yaml_tree.rb: fixing string quotation
  when dumping Ruby strings. Thanks Ingy

* test/psych/test_psych.rb: appropriate tests.

* test/psych/test_yaml.rb: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39144 b2dd03c8-39d4-4d8f-98ff-823fe69b080e