Large overhaul of everything to do with Gamma-distributed rate heterogeneity.  mutationRates are now operated on only by a DeltaExchange operator to guarantee a mean rate of 1.0.  A single Gamma distribution is shared by all rates.  Its scale parameter is fixed to be the reciprocal of its shape, and its shape is operated on by a ScaleOperator, with a fixed Exponential prior.  Thanks to Remco for advice on this\!
Large overhaul of everything to do with Gamma-distributed rate heterogeneity.  mutationRates are now operated on only by a DeltaExchange operator to guarantee a mean rate of 1.0.  A single Gamma distribution is shared by all rates.  Its scale parameter is fixed to be the reciprocal of its shape, and its shape is operated on by a ScaleOperator, with a fixed Exponential prior.  Thanks to Remco for advice on this\!

lmaurits/BEASTling