Changing the behavior of centroid disulfide detection.
Previously, disulf detection in centroid used CEN-CB distance when detecting disulfides. This leads to problems in symmetric structures where disulfides across symm interfaces are not detected symmetrically (since the distance of CEN_i to CB_j != distance of CB_i to CEN_j). According to the comments in the code, the check should be using CB-CB dist, so I am changing the behavior to that. The behavior is changed for both symmetric and asymmetric poses to be consistent.