stop_list.c: various minor fixes
stop_list.c: various minor fixes

Fixes the type of dist to match the return type of prv_dist_sq, to fix
the integer overflow that still exists.  Also removes another magic
number.

edmundnoble/pebble-caltrain,ashneo76/pebble-caltrain,dwfreed/pebble-caltrain,wowza512/s,ashneo76/pebble-caltrain,dwfreed/pebble-caltrain,edmundnoble/pebble-caltrain,wowza512/s,ashneo76/pebble-caltrain,edmundnoble/pebble-caltrain,Katharine/pebble-caltrain,Katharine/pebble-caltrain,dwfreed/pebble-caltrain,Katharine/pebble-caltrain,dwfreed/pebble-caltrain,ashneo76/pebble-caltrain,wowza512/s,Katharine/pebble-caltrain,wowza512/s,edmundnoble/pebble-caltrain