 collector to track which heap pages (assumed to be
a multiple of the collectors block size) have been written during
a certain time interval.  The collector provides several
implementations, which might be adapted.  The default
(<TT>DEFAULT_VDB</tt>) is a placeholder which treats all pages
as having been written.  This ensures correctness, but renders
incremental and generational collection essentially useless.
<H2>Stack traces for debug support</h2>
If stack traces in objects are need for debug support,
<