title: Why would yaml be unavailable in production?
body: <p>On my OS X development system:</p>
  
  <pre><code>$ ruby --version
  ruby 1.8.6 (2007-03-13 patchlevel 0) [universal-darwin8.0]
  
  $ script/console
  Loading development environment (Rails 2.3.4)
  &gt;&gt; require 'yaml'
  =&gt; []
  </code></pre>
  
  <p>On CentOS 5.3 production system:</p>
  
  <pre><code>$ script/console production
  Loading production environment (Rails 2.3.4)
  /opt/ruby-enterprise-1.8.7-2009.10/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/base.rb:1959:in `method_missing':NoMethodError: undefined method `define_index' for #&lt;Class:0x2e6f7b0&gt;
  &gt;&gt; require 'yaml'
  =&gt; false
  </code></pre>
  
  <p>Anything I can do about that NoMethodError?</p>
  
  <p>Why would yaml be unavailable. Isn't it part of the core Ruby libraries?</p>