Fix up null potential handling. Collision time must rever to the null collision time unless the atom had a real collision. Fix up debugging output as well.
Fix up null potential handling. Collision time must rever to the null collision time unless the atom had a real collision.
Fix up debugging output as well.

ajschult/etomica,etomica/etomica,etomica/etomica,ajschult/etomica,ajschult/etomica,etomica/etomica