title: Apex AddError to SObject field
body: <p>Has anyone found a way of adding a dynamic field level error to an sobject?</p>
  
  <p>I would like to do something like</p>
  
  <pre><code>mySobjectRec.get('fieldname').addError('my error message');
  </code></pre>
  
  <p>I realise that mySobjectRec.fieldname__c.addError('my error message') works.</p>