* optimization: modular arithmetic for a particular requested width
is implemented using a tagged representation unless a better
representation is available.
+ * bug fix: FIND-CLASS was not thread-safe. (reported by Attila Lendvai)
* bug fix: ~R was broken for vigtillions. (thanks to Luis Oliveira)
* bug fix: attempt to obtain *SCHEDULER-LOCK* recursively when
unscheduling timer at the same time as another timer fires.