Alpha 4 patch 6 hotfix 3

Added/changed:

• Another bunch of small optimizations

• Added a message if no export stock on wagon arrival

• Messengers from river towns will not visit in winter now

Fixed:

• Trading boats had water in them if post-processing turned off

• Crash after relocating animals

• It was possible to build smeltery with entrance on water

• Crash when hovering smeltery (in rare cases)

• Could create a house with blocked entrance leading to white lines

• Foresters stopped chopping trees in some of the previous versions

• A few more cases of false "inaccessible"

• A few more cases of white lines