.  Garbage collection is triggered
whenever we notice that more than
<TT>GC_heap_size</tt>/2 * <TT>GC_free_space_divisor</tt>
bytes of allocation have taken place.
After <TT>GC_full_freq</tt> minor collections a major collection
is started.
<P>
All collections initially run interrupted until a predetermined
amount of time (50 msecs by default) has expired.  If this allows
the collection to complete entirely, we can avoid correcting
for data structure modifications during the collection.  If it does
not comp