title: Mark deprecated fields in WCF contract
body: <p>I have a wcf contract that works with client v1. </p>
  
  <p>Now I'm working on service v2, and i want to mark some of the fields as deprecated, So client v1 will see and use them, and client v2 will ignore them.</p>
  
  <p>Are there any best practices for this issue? Are there any existing attributes in WCF that i should use?</p>
  
  <p>thanks.</p>