Racket v5.2.1

Racket version 5.2.1 is now available from

  http://racket-lang.org/

* Performance improvements include the use of epoll()/kqueue()
  instead of select() for the Racket thread scheduler, cross-module
  inlining of small functions, and the use of SSE instead of x87 for
  JIT-compiled floating-point operations on platforms where SSE is
  always available (including x86_64 platforms).  A related change
  is the interning of literal numbers, strings, byte strings,
  characters, and regexps that appear in code and syntax objects.

* DrRacket uses a set of composable ray-traced icons available from
  the new `images' library collection.

* Typed Racket's `typecheck-fail' form allows macro creators to
  customize the error messages that Typed Racket produces.  This is
  especially useful when creating pattern matching macros.

* The performance of Redex's matcher has been substantially
  improved; depending on the model you should see improvements
  between 2x and 50x in the time it takes to reduce terms.

* Plots look nicer and are more correct at very small and very large
  scales.  New features include customizable dual axis ticks and
  transforms (e.g., log axes, date and currency ticks, axis interval
  collapse and stretch), stacked histograms, and 3D vector fields.
  The legacy `fit' function and libfit have been removed.

* The `2htdp/universe' library's `big-bang' form supports an