IMPORTANTWith the release update, Garry said that addons needs a little change to work in GMod 13.The little change, is that you will need to rename info.txt to addon.txt on all the addons you decide to keep after the switch. Its still suggested to only keep content addons unless you know what you are doing, and knows which addons works for GMod 13, and which doesn't.But you will still need to RENAME info.txt to addon.txt on ALL of your addons inside the addon folder.
SVNs and the other content packs will need updating so the file inside is addon.txt and not info.txt for when people download them.