Deal with divide by zero in the python stats stuff.
Deal with divide by zero in the python stats stuff.

util/stats/info.py:
    If an operation results in a divide by zero, just return None

pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-