[racket] Non-in-place installs for Racket from git

At Sun, 16 Mar 2014 14:44:27 +0800, WarGrey Gyoudmon Ju wrote:
> Now I figure out that, git version is in its way to support class system in
> Typed Racket,
> but  `raco install` via downloading only have the stable packages for
> stable versions.

Just to clarify, `raco pkg install` should work now that the
package-extraction service is restored.

If you use `raco pkg install` from a v6.0 distribution, it should still
get the old package version, because the distribution is configured to
check a v6.0-specific catalog first.