[plt-scheme] Planet submission

Hi all,

I've completed my first PLaneT update. I feel like a new person.

However, I wanted to ask if I "did the right thing." In particular, I
called my update a "non-backward compatible" update. Mostly, this is
because my update changed 'require' statements to reflect changes in
the web server collection ("servlet-sig.ss" to "sig.ss", it seems).

One solution would have been to use units to bind things late based on
version number. I took a different approach, and (hopefully) set the
minimum required version for the library to v370 or greater. This felt
like a non-backward-compatible change, so I said as much.

This was for the "xmlrpc" package, FWIW. I just wondered if this was,
in general, one of the kinds of changes one might consider as being
"backwards incompatible". Or, was there a better solution? (Naturally,
I begin to wonder why I didn't ask this question before doing the
commit...)

Cheers,
Matt