Archive does not support decreasing AUTO_INCREMENT,
since it does not support indexes (the PRIMARY KEY on
AUTO_INCREMENT is enforced by only allowing higher values than
the current max.)

Bug was that negative AUTO_INCREMENT was converted to unsigned
and become very large positive values instead.

Solution was to treat all negative AUTO_INCREMENT values as
(unsigned) 0. This means that one cannot insert negative values
into an AUTO_INCREMENT column in a Archive table.