neweff production: Consider insufficient food

neweff production: Consider insufficient food

newe() and prod() duplicate parts of the update's do_feed(), except
they round babies down instead of randomly, to get a stable,
conservative forecast.  Unlike the update, they assume sufficient
food.  Inaccurate for sectors that are going to starve or have
suboptimal population growth.  Not documented.  Has always been that
way.

Eliminate the undocumented assumption by replacing the duplicate code
by a call of do_feed().  Add a suitable parameter to do_feed() to
preserve the different rounding.

The update test shows the improvement.

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