title: How to check in a Validator if the value has been changed?
body: <p>I know I can get the old value through <code>UIInput#getValue()</code>.</p>
  
  <p>But in many cases where the field is bound to a bean value I want to get the default value that I don't need to validate if the input equals the default value. </p>
  
  <p>This is very usefull if a certain field has a unique constraint and you have a editing form.<br>
  Validation will always fail since in a check constraint method it will always find its own value thus validating to false.  </p>
  
  <p>One way would be to pass that default value as an attribute using <code>&lt;f:attribute&gt;</code> and check inside the validator. But is there an easier built-in way?</p>