Experimental changes to track zero-pages (pages full of zeros)

The changes:

 o) The number of zero pages is tracked in the TOTAL_MEM counter on free.  The DEBUG mode is used in order to get to the stack frame of the malloc that corresponds to the free.

 o) The number of zero pages is also tracked in the leak counter of MEM_LIVE, so using the live dump sentinel (igprof -D) one can analyze the heap in the middle of a reconstruction run.

 o) Fresh memory is initialized to 1.  That should avoid counting unused malloc (which is not so bad) as compared to 0-set memory.