For future releases?
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- JDT:  In Recluster, change "single" to an enum for user clarity?
  [do we have any other option that "sungle" or "subjets"]
- JDT:  Should we have a FASTJET_CONTRIB_BEGIN_NAMESPACE?  It would
  help those of us who use XCode to edit, which is aggressive about
  auto-indenting. [Consider this for the full contrib??]
- More generic kinematic cuts?