Index: wp-includes/post-thumbnail-template.php
===================================================================
--- wp-includes/post-thumbnail-template.php	(revision 17545)
+++ wp-includes/post-thumbnail-template.php	(working copy)
@@ -70,4 +70,23 @@
 	return apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr );
 }
 
-?>
+/**
+ * Retrieve Post Thumbnail URL.
+ *
+ * @param int $post_id Optional. Post ID.
+ * @param string $size Optional. Image size. Defaults to 'post-thumbnail'.
+ */
+function get_the_post_thumbnail_src( $post_id = NULL, $size = 'post-thumbnail' ) {
+	$post_id = ( NULL === $post_id ) ? get_the_ID() : $post_id;
+	$post_thumbnail_id = get_post_thumbnail_id( $post_id );
+
+	if ( $post_thumbnail_id ) {
+		$size = apply_filters( 'post_thumbnail_size', $size );
+		list( $src ) = wp_get_attachment_image_src( $post_thumbnail_id, $size );
+	} else {
+		$src = false;
+	}
+
+	return apply_filters( 'post_thumbnail_src', $src, $post_id, $post_thumbnail_id, $size, $icon );
+}
+