update/revolt: Make security bonus proportional to efficiency

update/revolt: Make security bonus proportional to efficiency

Land units with capability security get a combat bonus regardless of
efficiency.  This lets players get the benefits of a security unit at
a discount: just don't build it beyond 10%.

Multiply the combat bonus by eff/100.  Together with the previous
commit, this closes bug#64.

Note that the the strength of a security unit's commando raid is
already proportional to its efficiency.

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