title: Using `dynamic` keyword in C# doesn't compile
body: <p>I'm trying to compile a piece of C# code that contains the <code>dynamic</code> keyword.
  (I need this keyword for using ironpython.)
  However, it doesn't compile, complaining that </p>
  
  <pre><code>error CS1980: Dynamic keyword requires 
  `System.Runtime.CompilerServices.DynamicAttribute' to be defined.
  Are you missing System.Core.dll assembly reference?
  </code></pre>
  
  <p>The compiler I'm using is <code>Mono JIT compiler version 2.10.8.1</code>.
  I don't have <code>System.Runtime.CompilerServices.DynamicAttribute</code> in the list of possible references.</p>
  
  <p>How can I make mono accept the <code>dynamic</code> keyword?</p>