title: Disable checking of overflow with Array.Sum
body: <p>There is a Pex4Fun problem that asks the user to write code that finds the sum of an array.</p>
  
  <pre><code>using System;
  using System.Linq;
  
  public class Program {
    public static int Puzzle(int[] a) {
      return a.Sum();
    }
  }
  </code></pre>
  
  <p>Pex expects that it can pass {-1840512878, -2147418112} and get back the underflowed number, 307036306, however the LINQ method, Array.Sum(), checks for overflow.</p>
  
  <p>I can't use the unchecked keyword around the method invocation of a.Sum() because the addition happens inside of the method.</p>
  
  <p>Is there any way to disable the checking of underflow/overflow with Array.Sum()?</p>