title: Marshalling error when caching models with date prior to 1900
body: <p>I have some active record models which have a "published_on" attribute.  When I attempt to cache models with a published_on date prior to 1/1/1900, I get an error such as: </p>
  
  <pre><code>Marshalling error for key 'popular_products': year too big to marshal: 1300 UTC
  You are trying to cache a Ruby object which cannot be serialized to memcached.
  </code></pre>
  
  <p>I can reproduce a similar error with ruby:</p>
  
  <pre><code>irb(main)&gt; Marshal.dump( Time.parse("1/1/1900") )
  ArgumentError: year too big to marshal: 1899 UTC
  </code></pre>
  
  <p>What's the right approach for caching models with dates prior to 1900? </p>