[jdev] add a nickname at subscribtion time

[Remko Tronçon]

Hi Paul,

> <presence to='134 at myserver.com' type='subscribe'>
>     <nick xmlns='http://jabber.org/protocol/nick'>paul</nick>
> </presence>

It is up to the client to use this information when acknowledging the
subscription (e.g. to rename the roster item). If the client you use
doesn't support this (or doesn't show this), this information will be
thrown away.

cheers,
Remko