title: Adding extra information to a custom exception
body: <p>I've created a custom exception for a very specific problem that can go wrong. I receive data from another system, and I raise the exception if it bombs while trying to parse that data. In my custom exception, I added a field called "ResponseData", so I can track exactly what my code couldn't handle.</p>
  
  <p>In custom exceptions such as this one, should that extra response data go into the exception "message"? If it goes there, the message could be huge. I kind of want it there because I'm using Elmah, and that's how I can get at that data.</p>
  
  <p>So the question is either:
  - How can I get Elmah to record extra information from a field in a custom exception
  OR
  - Should extra exception details go into the "message" property?</p>