Left 4 Dead 2 - Update

An update has been released for Left 4 Dead 2.

Tweaks to add-on management:
- Report conflicts between mission scripts in the Add-ons menu.
- Fixed checked items getting unchecked after reporting a conflict.
- Allow all add-ons to override base content at the main menu.
- Allow content-only add-ons on non-vanilla dedicated servers.
- Allow add-ons to override base mission and mode scripts on non-vanilla servers.