From Michael Fitzegerald Between grading papers and dreaming of Mexico, the Admiral and I try to get plenty of exercise by walking, riding our bikes and heading to the Capital Athletic Club where the Admiral and I go almost every day for swimming and to work on the machines. (OK. I don't go on the machines at all, but I do try to get in a quarter-mile of thrashing through the water. And, no, I missed today, but...) In my walk this afternoon (to make up for skipping my swim), I ran across a house (506 S Street) a block away that was being torn down, a 100-plus year old casa that had been taken over by some local homeless people. For California, the demolition guys were pretty casual with