We gasped at the sight: the San Francisco Public Library's Bookmobile cozying up to our favorite El Tonayense truck on Harrison near 20th. Now we truly have everything we need. Well, almost. Maybe the folks at Cafe Gratitude will let us us the restroom. A recent ">Los Angeles Times op-ed called taco trucks "oases of meat and cheer in the night" -- an allusion, perhaps, to those famous early lines of Virgil's Aeneid: The......