add_action('init', 'demo_register_post_type');

function demo_register_post_type() {
    register_post_type('tribe_events', array( 'rewrite' => array('slug' => 'event', 'with_front' => false),
        'labels' => array(
            'name' => 'Demos',
            'singular_name' => 'Demo',
            'add_new' => 'Add new demo',
            'edit_item' => 'Edit demo',
            'new_item' => 'New demo',
            'view_item' => 'View demo',
            'search_items' => 'Search demos',
            'not_found' => 'No demos found',
            'not_found_in_trash' => 'No demos found in Trash'
        ),
        'public' => true,
        'supports' => array(
            'title',
            'excerpt'
        ),
        'taxonomies' => array('category', 'post_tag') // this is IMPORTANT
    ));
}


add_filter('pre_get_posts', 'query_post_type');
function query_post_type($query) {
  if(is_archive() || is_tag() || is_home() && empty( $query->query_vars['suppress_filters'] ) ) {
    $post_type = get_query_var('post_type');
	if($post_type)
	    $post_type = $post_type;
	else
	    $post_type = array('post','tribe_events','attachment');
    $query->set('post_type',$post_type);
	return $query;
    }
}