(prod): Change variable work from double to int. This matches actual

(prod): Change variable work from double to int.  This matches actual
production code better, and fixes a small inaccuracy introduced in
rev. 1.10.

(prod): Production is limited to 999 units.  Fix for production
efficiency > 1, e.g. agribusiness.

(prod): Raw material consumption was incorrectly limited to 999.

(prod): Production backlog was handled incorrectly; it claimed `will
make' lots, `max' less, which is backwards.