Removed the policy control for what to do beyond the domain.
Old behaviour was constant extrapolation, current behaviour
is linear extrapolation. The possibility to choose was never
needed and has beem removed.
Recall that the class that used to be called SinglePvtDead has
been renamed to SinglePvtDeadSpline. If 'props_use_spline' is true,
that class is used (this is the default), which makes a monotone
spline that is uniformly, densely sampled. The new class simply
uses linear interpolation in the input tables.