This was kind of a PITA on Linux Mint Maya. I had to uninstall libcurl4-openssl-dev to install libcurl4-nss in order to get liboauth-dev to install. And after applying that second patch, I was able to get it to compile and run.
I think I'm going to give up. I can't get the client to authenticate the server and most of the options I'm trying for language and directory aren't being recognized.
I wish, Mr. Gog would get over the NIH and just allow us to use a proper FTP client.
...or go one step further and do as the Humble Bundle guys do and offer torrents backed by HTTP web seeds. Private torrent trackers have already proven that it's not difficult to prevent unauthorized downloaders. (Generate the torrent file dynamically so each user's torrent client can announce itself using a token analogous to the cookie they currently use for HTTP downloads and set the "private" bit so torrent clients only find peers via the GOG tracker. Then, tell users that sharing their torrent file will be punished according to the same rules as sharing their login info.)
Not only would that give efficient chunk-level checksumming and resume/redownload for free while still giving them the ability to block attempts to share the download links with the world, it'd allow them to save bandwidth whenever more than one person is grabbing the same game at the same time and it'd provide a natural way to handle choosing whether or not to download extras on a piece-by-piece basis.
(Seriously. What modern torrent client doesn't
have the option to let you pick files within a torrent before it starts downloading?)