Speed up build process.

Hi, 

Since we are dealing with quite heavy folders we need to be carefully what we do with them. What I have done is to reuse old archive and just update it, generally only few files are changed and repacking whole archive is wast of time. Additionally, I've removed copying. I understand the idea, but well copying almost 1,5GB every time is little overkill. You can always do that manually for the spacial occasions like releases, but in daily use it is little bit too much in my opinion.