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

Below is the second draft of the release announcement items for
v5.2.1. Let me know if I've missed something.

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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.

* 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.

* 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.

* The `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 `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.)

* 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'.

* 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.

* Plots look nicer, render up to 4 times faster, 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.

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