title: C#/MEF don't work with [ImportingConstrutor] with default values
body: <p>I have more or less the same problem as in this question:
  <a href="https://stackoverflow.com/questions/9023098/c-mef-doesnt-work-with-a-base-class-without-parameterless-constructor">C#/MEF doesn&#39;t work with a base class without parameterless constructor</a></p>
  
  <p>I understand the answer as well. MEF doesn't know a value for val so its not able to create an instance.</p>
  
  <p>But I have no base ctor call and a default value for val:</p>
  
  <pre><code>[Export(typeof(IPrimitiveDecomposer))]
  public class Prim : IPrimitiveDecomposer
  {
      [ImportingConstructor] 
      public Prim(int val=0)
      {//some code
      }
  
      public bool Match(Node node) {return true;}
  }
  </code></pre>
  
  <p>The code compiles fine, but MEF doesn't seem to have an export for IPrimitiveDecomposer when I ask for it.
  When I do the following all works fine:</p>
  
  <pre><code>[Export(typeof(IPrimitiveDecomposer))]
  public class Prim : IPrimitiveDecomposer
  {
      public Prim() : this(0)
      public Prim(int val=0)
      {//some code
      }
  
      public bool Match(Node node) {return true;}
  }
  </code></pre>
  
  <p>thx for your help
  Soko</p>