fix for #42

the pressing memory issues should now be gone.

I'm not so deep into the architecture. Maybe, for the future and future updates, it would be a good idea to move UpdateUnits() and UpdateMapFeatures() to something that is called every frame (because basically the are called too often, but that is checked, and every function doing something with unitvectors or mapfeature vector has to call them in advance). But current version works fine, too. :)