This is a complete port of the S package ppr which provides
a formula-based replacement for ppreg(). It has been 
converted to double precision, and as the underlying Fortran code
is very sensitive to rounding, will give different answers.

98/08/23: the smoothing spline code will now work. As it was almost
completely needed here, I have added a port of smooth.spline using the
public-domain `gamfit' code of T. Hastie and R. Tibshirani
(statlib/general/gamfit).

supsmu is available as a standalone function.

