pub fn keep_previous(path: &Path)Expand description
Before another table takes path’s place (a training here, another
device’s table through the sharing): the one there, when this Sioul can
use it, copied beside as table.prev.bin (written beside, then moved).
A table this Sioul refuses then leaves the last good one in use
(Table::cached), and never takes its place there. Best effort: a copy
that fails leaves the one before as it was.