Relic's mildly disappointing orc-eviscerating game Space Marine is getting a 4-player co-op mode later this month, with THQ dating the roll out of the free upgrade for the 25th. It's called EXTERMINATUS. Which, quite coincidentally, is my middle name. There will be two scenarios in this mini-expansion, in which you can play as tactical marines, heavy-weaponised devastators or whoosh-bam marines. You'll be fighting orcs and…