Add sxml->string/internal

scheme/httpd/surflets/sxml.scm

@@ -32,6 +32,9 @@
       (pre-post-order sxml-tree rules) 
       port))))
 
+(define (sxml->string/internal sxml-tree rules)
+  (list (sxml->string sxml-tree rules)))
+
 ;; Predicate for attributes in sxml.
 (define (sxml-attribute? thing)
   (and (pair? thing)