lete, we return control to the mutator, and perform small
amounts of additional GC work during those later allocations that
cannot be satisfied from small object free lists. When marking completes,
the set of modified pages is retrieved, and we mark once again from
marked objects on those pages, this time with the mutator stopped.
<P>
We keep track of modified pages using one of several distinct mechanisms:
<OL>
<LI>
Through explicit mutator cooperation.  Currently this requires
the use of <TT>GC_malloc_stu