[racket] Racket v5.93

Racket v5.93 is now available from

   http://racket-lang.org/

Version 5.93 repairs a few problems with the recent v5.92 release (in
preparation for a v6.0 release):

  * fixed a low-level concurrency problem with the GUI library for Mac
    OS X, which especially affected 32-bit builds;

  * fixed GRacket-based launchers (such as `drracket`) in a Unix-style
    installation;

  * expanded the list of recognized OpenSSL library versions;

  * fixed small CSS problems and inconsistencies (relative to v5.3.6) in
    the new Scribble style as used by the Racket documentation; and

  * added the version number back to the "racket" directory within the
    source distribution bundle.