X-UA-Compatible value IE=edge must be in header to pass w3c validation

The X-UA-Compatible http-equiv meta tag added by advagg_preprocess_html() method fails to validate in W3C validator.

If you're looking to make it technically valid (everyone loves to see the green favicon) w/o effecting any functionality, you should be able to just wrap it in a "if IE" tag.

The meta_ie_render_engine should be modified to add prefix and suffix as below

// Setup IE meta tag to force IE rendering mode.
  $meta_ie_render_engine = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'http-equiv' => 'X-UA-Compatible',
      'content' =>  'IE=edge,chrome=1',
    ),
    '#weight' => '-99999',
    '#prefix' => '<!--[if IE]>',
    '#suffix' => '<![endif]-->',
  );