[racket-dev] sporadic failure when building PLaneT docs

Matthew pointed out that current-module-declare-name might play a role
and, sure enough, that was the problem. I've pushed a fix to planet
(since the resolver should be setting that back to #f before starting
the setup process), but probably the sandbox should also work when
that is set to something funny, so I sent in a PR for that one.

Robby