Lunch trades outlawed to protect kids with allergies ORMONDALE SCHOOL JOINS THOSE THAT HAVE APPLIED TIGHTER RULES By Kim Vo Mercury News In the underground economy of school lunches, third-grader Siobhan Rickert explained, the demands are straightforward: ``If you give me this cookie, I'll give you this pretzel.'' But no more. This month, Ormondale School in Portola Valley began cracking down on lunch swaps. No more trading mom's turkey sandwich for a peanut butter and jelly -- or exchanging chocolate chip cookies for, well, just about anything you want. Ormondale joins a smattering of Bay Area schools that have banned...