title: (tricky?) validation for a sfWidgetFormChoice form widget in Symfony
body: <p>I am using Symfony 1.3.2 with Propel ORM on Ubuntu 9.10. </p>
  
  <p>I am writing a registration form, which requires a user to provide a user name.</p>
  
  <p>I want to impose the following restrictions on the choice of names:</p>
  
  <ol>
  <li>That the name is unique (i.e. is not already in use by someone else</li>
  <li>The name is not in a list of offensive names, stored in a database table</li>
  </ol>
  
  <p>For the first requirement, it is easily done by using the sfValidatorPropelUnique validator.</p>
  
  <p>The challenge however lies in implementing the second requirement AND COMBINING requirement 1 and 2 into a single validator.</p>
  
  <p>I suppose I could write a custom validator to do this, but I am wondering is there a better way to do this (i.e. using the framework, and not "rolling my own" solution ?</p>