title: No error from Typescript compiler when constructor receives different parameters types as the ones from the implemented interface
body: <p>I have tried the following code:</p>
  
  <pre><code>interface IRectangle {
      height: number;
      width: number;
      getArea: ()=&gt;number;
  }
  
  module Shapes {
      export class Rectangle implements IRectangle {
          constructor(public height, public width) {
          }
  
          getArea() {
              return this.width * this.height;
          }
      }
  }
  
  console.log(new Shapes.Rectangle(12, 'a').getArea());
  </code></pre>
  
  <p>I'm expecting that the typescript compiler should give me an error when trying to supply a character to the constructor (last code line) even tough the interface (IRectangle) says that both fields should be of type number. But I don't receive any error. Why is the reason behind this behaviour?</p>