Handle the strange implementation of BDSS ignoring tree operator

[walterxie]

It seems BDSS https://github.com/fkmendes/bdtree/tree/master ignores tree root operator and scale operator, if the XML BDSS is given one value below:

<distribution id="BirthDeathSequentialSampling" spec="bdtree.likelihood.BirthDeathSequentialSampling" rootAge="81.34374515244996" tree="@psi">

So, only when the above XML is change to use lower="1.0" upper="100.0", these two tree operators are working.

[walterxie]

The problem is how to find the Generator's bound for any distributions if not uniform?

[walterxie]

Not sure why we need MRCAPrior. BirthDeathSequentialSampling does not have this input.