Ruby » Ruby master

• ext/psych/lib/psych/visitors/yaml_tree.rb: dump empty symbols with a
  tag so that they can be parsed on input. [Bug #9873] [ruby-core:62825]
• test/psych/test_symbol.rb: test for change

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46358 b2dd03c8-39d4-4d8f-98ff-823fe69b080e