Day of Defeat: Source update fixes Linux asset loading, map cycle

A new Day of Defeat: Source update has been released. It will apply automatically when you restart the game. Security and stability improvements headline the patch, along with fixes for Linux servers and custom maps.

• Fixed an incorrect check on Linux servers when setting the winter holiday active (community fix from Irineu).
• Fixed a bug where certain custom maps would not load assets correctly on Linux.
• Fixed servers skipping maps in the map cycle because ChangeLevel was being called multiple times.