Fixed|Unix: Crash when launching application (UnixInfo)

UnixInfo needed to know the application's /etc path, but the application
had not been fully constructed at the time.
UI|Client: Added "24-bit" color depth to Video Settings
UI|Client: Store game selection subset fold state persistently
Fixed|Windows: Missing exports and OpenGLGL API callback
Merge remote-tracking branch 'origin/master' into sdk-split
libgui|Cleanup: Removed ARB_debug_output

This extension wasn't in use and seems to be subtly differently defined
on different platforms.
Cleanup|qmake|64-bit: Preprocessor symbol for 64-bit builds

Conforming to naming conventions.