John's Grill celebrated its hundredth birthday a few weeks ago, and as a longtime fan of Old San Francisco and the works of Dashiell Hammett, I made sure to help observe the occasion. Hammett figures into the equation because at one point in his magnum opus, "The Maltese Falcon," gumshoe Sam Spade ducks into John's for a quick meal of chops, potatoes and sliced tomatoes before heading to Burlingame on a bum steer. I myself was on the trail of one of the 8-cent martinis the bar would be offering