Overnight trading was mixed in terms of price action and unenthusiastic in terms of mood. Word of an agreement between the U.S. and Mexico on ways to change the terms of NAFTA had little market impact, even though Mexico is currently the biggest overall customer for U.S. grains, soybeans and products combined. As an aside, how negotiations with Canada proceed will be very interesting. U.S. trade policies are currently tilted toward protectionism, but the U.S. will press Canada to give up policies that protect its dairy industry, policies Canada has vowed to defend and maintain.   Soybean futures prices continued their supply-driven sinking spell during the day session while corn prices slowly worked lower. Wheat prices traded bot...