More detailed description of these commits:
1) FSO: add notification for PXO firewall test
A very important step for multi. Any PXO game will now automatically inform the player about whether the game they started is discoverable by other players or not. The message is displayed in the chat screen.
2) FSO: fix game announcement issue causing first firewall check to fail
A minor fix for the previous commit.
3) FSO: add variant of game update packet to tell PXO we want firewall status
Another minor fix for the first commit in this nightly.
4) FSO: add weapon ambient sound (#3452)
Adds a new ambient sound for all weapons, not just player weapons. Enabled with the "$AmbientSnd:" option in the weapon table, and goes after the "$FlyBySnd:" entry.