riset: use truncated VSOP87 in riset()

* riset: use truncated VSOP87 in riset():
  * affects Sun only: saves ~43% CPU time
riset: use truncated VSOP87 in riset_ipol()

* riset: use truncated VSOP87 in riset_ipol():
  * affects planets only: saves ~50% CPU time
planet: use truncated VSOP87 in planet_position_la()