A couple of bugs

The techs that are supposed to reduce the manufacturing cost of ship defenses have a positive instead of negative multiplier value (for example see HighEfficiencyDeflector).

There are multiple places where signed 32 bit integers are used without overflow checking. Items I've identified so far: treasury credits, total production per turn of wealth, manufacturing, and research. I deliberately created ridiculously overpowered improvements to be able to test this, but in a very long game in a huge galaxy it could become an issue.