By Mark Alexander Ex·o·dus, noun: a mass departure of people... I read last week that Nancy Pelosi's hometown of San Francisco has a "zero waste goal" of keeping 80% of its human detritus out of landfills. I am sure this is gratifying to her suburban white-privileged supporters, but for those who are not in San Fran Nan's high-income class, Pelosiville has become the continental poop capital. That is a distinction it has held for three years now, and some blocks in this once fair city now look and smell like Calcutta. When you aren't avoiding panhandlers and thugs, you've got to be careful not to step on hypodermic needles or in human waste.