I added the statusnet: prefix to the xml output. This prefix should
be declared on the root element of all relevant XML output.
I also added two StatusNet-specific fields:
* statusnet:html - rendered HTML. Clients shouldn't have to guess
at the correct HTML rendering for notices, especially since some
of the links depend on context.
* statusnet:profile_url - profile URL for a user. You can't count
on a user being a local user in a distributed microblogging world.
So, this shows the explicit profile_url.
* respect count instead of listing all groups
* respect page parameter
* don't spew notice on undefined $id
* don't spew notice on undefined $group->homepage_url (dropped the element since there's nothing to go in it)
