I'm not trying to sound rude, but you might have to go directly to the source for this. I can think of how it could be done. You would need a variable that tallies peoples kill within a single life. We already have one to do that for total kills, just not one for a single streak. Problem is, I don't think that there is a variable defined within the source coding that will call that information. I do not believe that it will be too difficult to do though.
On a second note, and probably a more difficult one, would be the killstreak rewards. Sauerbraten doesn't (and most likely won't for a while) have anything comparable to Call of Duty killstreaks. However, it may be possible to give the players a small bonus, such as a Quaddamage, or a 30 second health bonus.
Sorry I can't be of much help :P when it comes to Sauerbraten, I only use coding that is beneficial to single player maps.