[IMP-dev] Nonbonded list

[Daniel Russel <drussel@gmail.com>]

The nonbonded list reports pairs of particles based on the distance 
between their centers. This is fine as long as all spheres have roughly 
the same radius. However, if some spheres are much larger than others, 
then we have problems as the sphere distance may be small when the 
center distance is large. Offhand, I don't have a simple solution to 
this problem.