title: Typescript class.default is not a constructor
body: <p>Creating an Angular2 app, I am facing the following problem, when calling the constructor of another class inside the constructor of first class.</p>
  
  <p>First Class code</p>
  
  <pre><code>import SecondClass from './second-class'
  
  export class FirstClass {
      someVar:string;
      secondClass:SecondClass;
  
      constructor(firstClass?: FirstClass) {
          someVar='test';
          secondClass= new SecondClass;
      }
  }
  </code></pre>
  
  <p>Second Class code:</p>
  
  <pre><code>export class SecondClass {
      someOtherVar:string;
  
      constructor(secondClass?:SecondClass) {
          someOtherVar='test';
      }
  }
  </code></pre>
  
  <p>Would give me the error: ORIGINAL EXCEPTION: TypeError: second_class_1.default is not a constructor</p>
  
  <p>Content of ./second-class</p>
  
  <pre><code>System.register([], function(exports_1, context_1) {
      "use strict";
      var __moduleName = context_1 &amp;&amp; context_1.id;
      var SecondClass;
      return {
          setters:[],
          execute: function() {
              SecondClass = (function () {
                  function SecondClass(secondClass) {
                      this.someOtherVar='test';
                  }
                  return SecondClass;
              }());
              exports_1("SecondClass", SecondClass);
          }
      }
  });
  //# sourceMappingURL=second-class.js.map
  </code></pre>
  
  <p>This is the compiled output from Typescript compiler</p>