Garry's Mod update - Fixes Lua execution exploit.

"We're releasing a small hotfix to address a recently found exploit that allowed users to execute arbitrary Lua scripts on servers. If you run a server, you should update it.

It's a very non-intrusive update, so there should be no risk of anything breaking, except - potentially - third-party binary modules."

This will break a lot of existing lua scripts that have somehow still managed to work up until now.