Update #4 - v1.839

As promised this update includes the following changes:

• an additional harder AI for skirmish

• new rocket soldier type with target following rockets

• option to quickly restart a finished game

• a defense building can be constructed in parallel with another building

• pressing unit group hotkeys twice will jump the camera to the next unit in the group

• double clicking on a unit will select all units with the same type in the sight of the camera

• shift/alt + drag selection won't reset previous unit selections

• Japanese comic localization fixes