j.f.chandler - 1976 july
override elliptic orbit calculations for bodies in fmmips
y-vectors are calculated as they are needed
jd   = input julian day number
fract= input fraction of day
yast(.,i)= output position for perturbing body i
ler     =  0 positions only needed for perturbing bodies
ler     =  1 velocities needed in relativity calculation
ler     =  2 velocities and accelerations needed in rel.cal.
note - present configuration assumes ler = 0