In the city of St. Louis, primary elections frequently have bigger consequences than general ones. But one item St. Louis voters will see on their Nov. 3 ballots could change that pattern in a big way: Proposition D. Touted by proponents as a minor change for voters that would mean big improvement for St. Louis, the measure would establish a nonpartisan election system for the offices of mayor, comptroller, the president of the Board of Aldermen and alderman.