[Owncloud] dev/unstable download

[Lukas Reschke]

> I have checked the official website/ftp/git (there are several branches
> but no 5.0). Blame on me if I overlooked it... :)

Master is always the upcoming version. So just checkout this branch.
(don't forget to add the apps + 3rdparty repositories as well)

An easier method may be to use our daily builds:
http://owncloud.org/releases/owncloud-daily-master.tar.bz2