title: FormControl ValueChanges event not firing when setValue is called
body: <p>I have the following code for an Angular 4 type-ahead component:
  There is a FormControl in the FormGroup which is tied with the html and it works perfectly.</p>
  
  <pre><code>this.ProfileForm.controls["code"]
  </code></pre>
  
  <p>The valueChanges event is firing when i change in the textbox. Now when i update the formcontrol value through programatically the valueChanges event is not firing.
  The following is the lines of code i written.</p>
  
  <pre><code>this.ProfileForm.controls["code"].setValue("someValue");
  
  this.ProfileForm.controls["code"].valueChanges.subscribe(() =&gt; {
              console.log("modified");}, () =&gt; { console.log("error") }, () =&gt; { console.log("completed") });
  </code></pre>
  
  <p>Any suggestion is appreciated.</p>