This update also include an update to the L4D2 Authoring Tools

- Added the Extended Mutation System
- Included demo EMS modes Holdout, Dash, L4D1
- Added support for Linux

- Server operators can now specify whether or not custom content is allowed when playing on their servers. This can be set on a per game mode basis – see cfg/addonconfig.cfg for details.

- Fixed yellow screen corruption that occurs on AMD Radeon HD 6000 Series hardware.
- Updated database to include video cards from the Steam survey through April 2013.

Add-ons
- If a found game is using a Mutation add-on from the workshop, the "Download Add-on" button will open the workshop page
- Adjusted add-on sorting when loading the main menu so Mutation add-ons can override UI elements.
- Reworked add-on management to improve stability and properly support custom mutations.
- Fixed the download progress panel sometimes not updating because it was referencing a different file than the one currently downloading.
- Added a drop-down menu to the add-on screen to filter by tags.
- Fixed occasional focus problem when clicking on the Addons list panel.
- Allow keyboard scrolling of the Addons list panel.

Publishing Tools
- Fixed published file browser not updating after publishing new content.
- Fixed published file browser showing only the first fifty items of a users workshop.
- Fixed upload tool throwing an error when replacing an existing file, if the file size was greater than the available space in the cloud.
- Fixed upload tool sometimes showing an error dialog for files that had been deleted from workshop.