Added a warning to ScaleOperator that warns the user the value of the parameter is 0.  ScaleOperators cannot move values of 0.  
Added a warning to ScaleOperator that warns the user the value of the parameter is 0.  ScaleOperators cannot move values of 0.  
JifengJiang/beast-mcmc,JifengJiang/beast-mcmc,JifengJiang/beast-mcmc,JifengJiang/beast-mcmc,JifengJiang/beast-mcmc