[jhc] darcs patch: clean up GC code, make distinction of po... (and 3 more)

Wed Apr 7 12:09:43 PDT 2010 John Meacham * clean up GC code, make distinction of pointers more type safe to catch errors Wed Apr 7 12:52:09 PDT 2010 John Meacham * add page cache for recently freed pages Wed Apr 7 17:15:45 PDT 2010 John Meacham * optimize and clean up code based on profiling Wed Apr 7 17:50:39 PDT 2010 John Meacham * get rid of special handling of the what_t in data and the needed bookeeping.