Well, I finally got rid of the brake squeal in my Volpe's front brakes. Toe-in, cleaning rims, scuffing rims, changing pads, etc. did not work and yet the rear brakes never squealed and the front brakes always squealed.
In trying to address any differences between the front and rear I noticed the rear brake cable housing hanger is much closer to the straddle cable than on the front brakes. I found a fork-crown-mounted cable housing stop made by Tektro at Harris Cyclery (
http://sheldonbrown.com/harris/cable...are-brake.html) and that seems to have solved the problem for me. I've gone two days now without frightening a single pedestrian.