* threads
** bug fix: parent thread now can be gc'ed even with a live
child thread
+ ** bug fix: binding a special with PROGV to no value is not
+ the same as that symbol not having been bound (thanks to
+ Hannu Koivisto)
* fixed some bugs revealed by Paul Dietz' test suite:
** ENSURE-GENERIC-FUNCTION should take a method class object for
the :method-class keyword argument.