subroutine BDREED - M.E.Ash  1969 Aug
n-body tape is read either forward or backward in time
observations in error records are skipped if ICT(31) so indicates
copy data to individual body arrays as indicated

on first entry, center-of-mass tape is not yet synched to
the n-body tape.  the two must have matching tabular
intervals and record epochs, but need not have the same
time spans -- we must line them up and mark them locked
together.  use jdcom(1) as flag for 1st c-of-m tape read.
(we also have jd=0.)