title: Using valdiation error messages to return warnings
body: <p>In datamapper you can use <code>$u-&gt;error_message('custom', 'This is a custom error message.');</code> to set an error message when validation fails upon a save.</p>
  
  <p>However I would like to be able to use this method to return message even in cases when the validation did not strictly fail - like warning or status messages after a save, that I want to return to the user.</p>
  
  <p>Anyone knows a way to achieve this? </p>