I know open source drivers and Mesa are second-class citizens, and games are generally developed and tested using proprietary nvidia and fglrx drivers, (and I must be glad it was released to Linux at all), thus I must bear the burden in insisting using the free radeon driver.
Anyway, it won't do any harm in requesting in here a better support to Mesa and free drivers, and it may be that developers will look with better eyes to us. I know that ideally Mesa should support the "GLX_EXT_swap_control" extension, but it does not; instead it has these two extensions that serves the same purpose: "GLX_MESA_swap_control" and "GLX_SGI_swap_control". It would be cool if you could fallback to one of them if "GLX_EXT_swap_control" is not found.
Also, it will make no difference if I can not start the game. It seems to me that the problem reported in
this thread can be related to the fact people who experience it is using Mesa (I also suffer from it, so I was unable to start the game so far). Recently two games also released in Humble Bundle had problems in starting up when using Mesa, but the guys were able to track the issue:
https://bugzilla.icculus.org/show_bug.cgi?id=5315