Also it confuses me that shotwell is on http://www.archlinux.org as well as http://aur.archlinux.org
You can put any package in the AUR as long as it doesn't use the exact same name as some package from the official repos.
shotwell v. shotwell-git is fine.There are tons of such packages. There's usually just one version of a package in the official repos but the AUR can have multiple ones: -git, -light, -no-foo etc.
