(Portland, OR)  --  Police say they've arrested a man who was armed with a chainsaw and a knife when he held up a Plaid Pantry store in Southeast Portland.  Authorities say 34-year-old Jonathan Lee Lathrop entered the store on Southeast Woodstock Boulevard last night and attempted to rob it, but officers arrived shortly afterward and apprehended him.  KOIN-TV reported there was a car on fire next door to the store, but it hasn't been determined whether there was a connection to the holdup.