Changed ingame radio callsigns.

A change to the briefing. As some players noted, I should have been talking about squads, not platoons. This is now fixed! :)

Added a new trigger to detect when there are 4 enemy soldiers or less left in Charkia. When it triggers a countdown begins to end the mission. I hope this reduces the waiting time for the last tango to be found.

Fixed an error with callsign Archangel. It was waiting for a trigger that I had deleted and forgot to edit the helicopter's waypoint. Another update will follow soon to change the mission ending parameters a bit.