Sort clusters prior to correcting for shower overlap

Sort CaloClusterss by their transverse energy prior to correcting their energy for overlaps -- done to ensure that the results do not depend on the (accidental?) ordering of the input (eg. the ordering of the calo RawBanks inside the RawEvent).

Note that the results still depend on the order (as the fraction of a digit which is assigned to a cluster depends on the energy of the cluster, and the energy of the cluster depends on the assigned fractions), but by explicitly sorting the clusters first, at least it no longer depends on the 'external' ordering.