Explicitly acknowledging that world-update-value never changes the expression of a closure (because a gensym cannot appear as a constant) means that I can get better caching out of free-variables.  This improves DVL performance on the current tests by about 5x.
Explicitly acknowledging that world-update-value never changes the
expression of a closure (because a gensym cannot appear as a constant)
means that I can get better caching out of free-variables.  This
improves DVL performance on the current tests by about 5x.

axch/dysvunctional-language,axch/dysvunctional-language,axch/dysvunctional-language,axch/dysvunctional-language