fixed bug in potts function (function was more or less unused)
fixed bug in potts function (function was more or less unused)

opengm/opengm,opengm/opengm,DerThorsten/opengm,plstcharles/opengm,DerThorsten/opengm,plstcharles/opengm,DerThorsten/opengm,plstcharles/opengm,plstcharles/opengm,opengm/opengm,opengm/opengm,opengm/opengm,DerThorsten/opengm,plstcharles/opengm,DerThorsten/opengm