Hi Epenetus,
I've got Spine working for Cocos2d-x, I hope I can help out here.
I haven't bothered getting the example running yet, so I'll go through my steps now.
Open up the project, missing "cocos2d.h"
- take the cocos2d-x/cocos2dx folder contents from my git clone of cocos2d-x project, copy into spine-runtimes/spine-cocos2dx/cocos2dx folder
Get data from file(spineboy.atlas) failed!
I found that the setSearchPaths command was using the 'ipad' folder, which doesn't exist. I've made a change to AppMacros.h and submitted a pull request. Change AppMacros.h:64-67 to look like this:
static Resource smallResource = {cocos2d::CCSizeMake(480, 320), "iphone"};
static Resource mediumResource = {cocos2d::CCSizeMake(960, 640), "iphone-retina"};
static Resource largeResource = {cocos2d::CCSizeMake(1024, 768), "iphone-retina"};
static Resource extralargeResource = {cocos2d::CCSizeMake(2048, 1536), "iphone-retina"};
Then it ran.