* test/psych/helper.rb: envutil is not available outside Ruby, so
  port the functions from envutil to the test helper.

* test/psych/test_deprecated.rb: ditto

* test/psych/test_encoding.rb: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40749 b2dd03c8-39d4-4d8f-98ff-823fe69b080e