[racket-dev] The repository is now split

I've just push a change to the plt repository that removes almost all
the packages.

The split repositories are all in the `racket` organization on GitHub.
You can see them here: https://github.com/racket/

I *highly* recommend creating a new clone of the repository, and
re-running `make`. This will install all of the packages in
"main-distribution" and "main-distribution-test" from the package
catalog.

There are a number of problems with the current Makefile setup, which
we're working on fixing, but which you'll need to know about for a
little while (hopefully not more than today).

* If you specify an explicit set of PKGS on the `make` command line,
that will NOT work.
* If you have user-installed Planet packages, there may be errors.

If you encounter other errors, please let me know, either by replying
or by finding me on IRC.

If you run `make` and then you want to edit and commit to a package
such as "rackunit", run the following commands inside your git
checkout:

  $ mkdir extra-pkgs
  $ cd extra-pkgs
  $ raco pkg update --clone rackunit

That will create a git checkout in the extra-pkgs/rackunit directory.
The `extra-pkgs` directory is set up to be ignored by the top-level
git checkout, so it's a good place to put package checkouts.

This will almost certainly break our continuous integration systems
for a little while, but I'm working to get that fixed.

Everyone should feel free to commit to the split repositories or to
the main repository at this point -- we do not plan any git surgery
that would be harmed by that.

I'd especially like to thank Jay and Matthew for working hard to help
with this, including fixing things I've broken. :)

Sam