a users group matches himself by default

This is an edge case.
The default behavior for group changes slightly:
When creating user and passing a value to $user, while not
passing a value to $group, will now result in $group = $user, instead of
$group = $name.

manifests/user.pp

@@ -28,7 +28,7 @@
 define sftp_jail::user (
   $jail,
   $user  = $name,
-  $group = $name,
+  $group = $user,
 ) {
   file { "${jail}/home/${user}":
     ensure => 'directory',