http://github.com/nex3/arc/commit/111fa3c8f021c4abffc1526c88...
http://github.com/nex3/arc/commit/e4ba31f34f84cd946403541ca8...
According to the comment, there is a bug in MzScheme <371 which sets the sticky bit on *nix, so it may still be necessary to call system sometimes.
and (xdef 'which-os system-type).
T.
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