[racket-dev] package-system update

The documentation directory and collection directory should be
configurable, now.

Besides starting from the git repository, you could also try out the
new "source" snapshot:

  http://www.cs.utah.edu/plt/snapshots/

The label on the "Source" snapshots really should say something like
"kernel in source form, plus pre-built packages and documentation". The
"Minimal Racket" variant doesn't have any packages, but it has the core
collections pre-built, and installing a package from the main
distribution gets the package in pre-built form from the snapshot site.

I tried out the "Racket | Source" version, which took about one minute
to download (83 MB), about 3-4 minutes for `configure' plus `make', and
about 40 seconds for `make install'. After `make install', DrRacket was
ready to go, and all documentation (for the main distribution) was
available.