* threads
** bug fix: threads stacks belonging to dead threads are freed by the
next exiting thread, no need to gc to collect thread stacks anymore
** minor incompatible change: INTERRUPT-THREAD-ERROR-ERRNO removed
** WITH-RECURSIVE-LOCK can be nested in a WITH-MUTEX for the same lock
** bug fix: dynamic variable and thread start related gc lossage
* threads
** bug fix: threads stacks belonging to dead threads are freed by the
next exiting thread, no need to gc to collect thread stacks anymore
** minor incompatible change: INTERRUPT-THREAD-ERROR-ERRNO removed
** WITH-RECURSIVE-LOCK can be nested in a WITH-MUTEX for the same lock
** bug fix: dynamic variable and thread start related gc lossage