Get block bodies from other fast sync'd nodes (#1073)
Get block bodies from other fast sync'd nodes (#1073)

Previous code used to always get full blocks from archival peers.
Fast sync nodes shouldn't need to, other fast sync nodes have all
the history they need. This only uses archival nodes when blocks
are requested at a height that's older than the horizon.
yeastplume/grin,yeastplume/grin