Sets up the post object for preview based on the post autosave.

function _set_preview( $post ) {
	if ( ! is_object( $post ) ) {
		return $post;
	}

	$preview = wp_get_post_autosave( $post->ID );

	if ( is_object( $preview ) ) {
		$preview = sanitize_post( $preview );

		$post->post_content = $preview->post_content;
		$post->post_title   = $preview->post_title;
		$post->post_excerpt = $preview->post_excerpt;
	}

	add_filter( 'get_the_terms', '_wp_preview_terms_filter', 10, 3 );
	add_filter( 'get_post_metadata', '_wp_preview_post_thumbnail_filter', 10, 3 );

	return $post;
}