HOUSTON (AP) - The pilot of a private jet was warned the plane was flying low just before it crashed en route to a scheduled landing in Houston to pick up former President Bush, a federal investigator said Tuesday. An investigation is under way into the crash of the Gulfstream G-1159A jet, which went down Monday morning, killing a crew of three. The plane, which belonged to Jet Place Inc. of Tulsa, Okla., left Dallas an hour earlier and was to have picked up Bush, who lives in Houston, for a trip to Ecuador to give a speech at a...