misc: improve building alignment with the foundation

partial fix of #57... we still have work to do
![openage_2014-11-07_05-21-51_00](https://cloud.githubusercontent.com/assets/726447/4950198/6ca87086-6657-11e4-8397-c1a5b34309d0.png)
Regarding the rounding issue for even-sized objects that @thejj has mentioned:

What about a simple `drawpos = (this->startpos.to_phys2() + this->sizse.to_phys2() / 2).to_phys3()`