title: MatSort not working. Throws Error: MatSortHeader must be placed within a parent element with the MatSort directive
body: <p>After i specify the <strong>mat-sort-header</strong> attribute on matHeaderCellDef to create a Sortable table in Angular Material, getting the following error</p>
  
  <blockquote>
    <p>MatSortHeader must be placed within a parent element with the MatSort directive.</p>
  </blockquote>
  
  <pre><code>&lt;mat-table #table matSort [dataSource]="myHttpDataSource"&gt;
  ....
  &lt;ng-container matColumnDef="myColumnName"&gt;
  &lt;mat-header-cell *matHeaderCellDef mat-sort-header&gt;&lt;/mat-header-cell&gt;
  &lt;mat-cell *matCellDef="let row"&gt; {{row.somedetails}} &lt;/mat-cell&gt;
  &lt;/ng-container&gt;
  &lt;/mat-table&gt;
  </code></pre>
  
  <p>Any pointers/help appreciated</p>