subroutine xxrdbd - j.f.chandler - 1982 feb
read body constants from disk, test for availability of n-body
or s-body dataset.  if available, fill in controls.
if not available, set up individual integration data set number.

jtest= index of body in n-body list (-index if s-body) or 0
npxx=  planet number of desired body
itpxx= flag set to 0 if n-body or -1 if s-body or tape number
klxx=  index of requested body within input list (-3 to numpln)
jdx=   time tags for individual records on integration tape
intxx= tabular interval (assumed integer if planet)
idirxx=direction of integration: +1 or -1
kxx=   integration controls
xintx= tabular interval (floating point)
nkixx= number of partials integration controls
kixx=  partials integration controls
isbd=  index for s-body tape setup. s-body not allowed if zero.
xxcom= array of body constants to be read from disk