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// show post thumbnails in feeds
function fb_post_thumbnail_2_feeds( $content ) {

	if ( has_post_thumbnail( get_the_ID() ) ) 
		$content = '<div>' . get_the_post_thumbnail( get_the_ID() ) . '</div>' . $content;

	return $content;
}
add_filter( 'the_excerpt_rss', 'fb_post_thumbnail_2_feeds' );
add_filter( 'the_content_feed', 'fb_post_thumbnail_2_feeds' );