[bf1942] New build lag

[Ryan C. Gordon]

> Yeah, I have a similar set up and now I've noticed that I have about a 30
> to 60 ping when before I had only 1 to 2.

I'll sprinkle some more "check for more packet" calls around...currently
it's doing this once per server frame. I can't imagine that the second
thread would help _that_ much, but a few more strategically placed
update-checks wouldn't hurt.

(or maybe I'll put the server thread back in once I'm sure there's not a
race condition.)

--ryan.