[racket] Whalesong 1.11 released

Hi everyone,

Whalesong 1.11 is a bug-fix release that may slightly impact the
performance of Whalesong applications.

Changes:

    * Whalesong's will not release control to the browser during
long-running computations. Program output may be a little bit more
delayed as a result.

    * Miscellaneous bug fixes.

Rationale: under rare situations, Whalesong's process of yielding
control to the browser during long-running computations can break the
soundness of the evaluator.  Until I have a proper fix ready and
tested, I've turned off the preemptive yielding.  Unfortunately, as a
side effect, programs may appear not to be producing output to the
browser until a computation is complete.  I'll get this fixed as soon
as I have a better understanding of the problem.