Revert to by_price index when globally settling
Revert to by_price index when globally settling

Because all positions will be closed anyway, using which index
doesn't matter in terms of amounts, however, using another index may
change the ID of historical virtual operations, specifically,
`fill_order_operation` -- we usually try to avoid this.

bitshares/bitshares-2,bitshares/bitshares-2,bitshares/bitshares-2,bitshares/bitshares-2