[racket-dev] Release Announcement for v5.2.1, third draft

Below is the third (and hopefully final) draft of the release
announcement items for v5.2.1. Last call for comments.

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* 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
   experimental game pad key handler.

   (edu: The handler accepts a limited number of keys, similar to a
     game pad; the addition of a game-pad handler also overlays the
     attached game pad icon on the big-bang canvas. A compatible
     addition will appear in WeScheme.)

* The `db' library now supports nested transactions and PostgreSQL
   arrays. Bugs involving MySQL authentication and memory corruption
   in the SQLite bindings have been fixed.

* The Macro Stepper tool in DrRacket no longer executes a program
   after expanding it.

* In the DMdA teaching languages, infinite recursive signatures
   ("streams", for example) with no intervening `mixed' are now
   supported, and the signatures of record definitions without fields
   now have generators for use with `property'.

* MysterX's ActiveX support is deprecated and will be removed in
   the next release. MysterX's core COM functionality will become
   deprecated in the next release, but COM functionality will be
   supported for the foreseeable future as a compatibility layer
   over a forthcoming `ffi/com' library.

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