* ext/psych/lib/psych/visitors/yaml_tree.rb: fix NameError dumping and
  loading. Fixes GH #85. Thanks @brentdax for the patch!
* test/psych/test_exception.rb: test for fix

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47319 b2dd03c8-39d4-4d8f-98ff-823fe69b080e