title: Angular 2 can't find a component declared in my feature module
body: <p>I'm having a tough time getting modules to work in Angular 2.
  I have created <a href="http://plnkr.co/edit/gJup4zH7v4CoFNC8k5kZ?p=preview" rel="noreferrer">a plunk</a> that demonstrates the problem.
  In the plunk, you'll see I have app.module. This module imports app-common.module, which contains a component to display page headers. The template for the top level component, app.component contains the selector for this component.
  Here's app.common.module:</p>
  
  
  
  <pre class="lang-typescript prettyprint-override"><code>@NgModule({
  imports:[CommonModule, FormsModule],
  declarations: [PageHeaderComponent]
  })
  export class AppCommonModule { }
  </code></pre>
  
  <p>Here's app.module:</p>
  
  <pre class="lang-typescript prettyprint-override"><code>@NgModule({
  imports:      [AppCommonModule, BrowserModule],
  declarations: [AppComponent ],
  bootstrap:    [ AppComponent ]
  })
  export class AppModule { }
  </code></pre>
  
  <p>When the application is run, it throws an error that "ref-pageheader" is not a known element. If I declare the component in app.module, it works fine.
  So, why can't I declare this component in a module that gets imported into the main app.module? It seems Angular can't find it when this is done. What am I doing wrong? Am I missing something?</p>