patch indexing for (de)selected weights
This fixes an issue reported on the ATLAS Rivet list where the weight indices might get messed up when (de-)selected a subset of the weights.
At the same time, I've made the Event
class aware of the indices corresponding to the surviving weight subset and let it strip out deselected weights (as opposed to the AnalysisHandler
doing that like before). This simplifies the code in some other places, notably MC_WEIGHTS
and MC_XS
.