ash/becker  may 1968  subroutine emipt
code moved to jnitl/jlipt  1977 dec  j.f.chandler
subroutine emipt determines position and velocity in the encke
elliptic orbit and the partial derivatives of position and
velocity in this orbit with respect to the orbital elements
for target bodies
nn=0 position and velocity determined
nn=-1,1 position,velocity,and partial derivatives determined