Autoload is "thread safe" in modern rubies ([MRI >= 1.9.2][1], [JRuby >= 1.6.6][2], and [RBX (not sure exactly which version added this)][3]). There has been an autoload thread safety test in [RubySpec for two years][4] so any conformant ruby implementation must implement autoload in a thread safe manner.

I don't think there is any practical issue with always loading spec support stuff in production but it feels a little unclean. Let me know if you still feel that we should avoid `autoload`.

[1]: https://bugs.ruby-lang.org/issues/921#note-32
[2]: http://jira.codehaus.org/browse/JRUBY-3194?focusedCommentId=290605&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-290605
[3]: https://twitter.com/rubinius/status/360499679529672704
[4]: https://github.com/rubyspec/rubyspec/commit/f39daad184177b0b6706de993abd22601cea10d9