$onelevel versus $depth$1

[Michael Schwartz <mike@gluu.org>]

Markus asked why not use $depth$1 versus $onelevel?

1) $onelevel is a special case. Its the most common depth, so it deserves 
a special keyword.

2) Why do $depth and $onelevel have to be mutually exclusive?

3) I think its bad practice for servers to support $depth$1 and not 
$depth$2 etc. I'd rather the XDI server implemenations just say that 
$depth is supported or not supported, but not partially supported.

- Mike