Indices - local range weighted GiStar for label properties

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The Gi* calculations for the label properties currently weight each label only 
once in the calculation.  

A useful variant would be to weight each label by the number of groups within 
the neighbour set which contain them (calc_abc2).  Further, one could weight 
them by the abundances (calc_abc3)

The label property stats are written to allow weighting schemes, so it should 
be a case of calling the same functions but with calc_abc2/3 as relevant.  

Original issue reported on code.google.com by shawnlaffan on 20 Sep 2013 at 4:45