production: Use update code instead of duplicating it

production: Use update code instead of duplicating it

prod() duplicates the update's sector production code, except it
computes both output with present materials ("make" output) and output
not limited by lack of materials or production backlog ("max" output).
It also rounds materials consumed up instead of randomly.

Factor prod_output() out of produce() for reuse by prod().  prod()
runs it twice: once for "make" output and once for "max" output.

Test output changes are due to random rounding.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>