Fix file-responder directory listing problem

contrib/httpd/file-responder.factor

@@ -36,7 +36,7 @@ parser sequences strings ;
     ] if ;
 
 : serve-directory ( filename -- )
-    "/" over tail? [
+    dup "/" tail? [
         dup "index.html" append dup exists? [
             nip serve-file
         ] [

library/io/files.factor

@@ -6,7 +6,8 @@ styles ;
 
 ! Words for accessing filesystem meta-data.
 
-: path+ ( path path -- path ) "/" swap append3 ;
+: path+ ( path path -- path )
+    over "/" tail? [ append ] [ "/" swap append3 ] if ;
 
 : exists? ( file -- ? ) stat >boolean ;