Update callback interfaces so that the C part compiles.

I'm not sure why this helped, but moving the go*CB declarations out of glue.h and closer
to their usage fixes some "incompatible type with previous declaration" errors.
Fix so that it builds with Go 1.1.1

Remove references to os.EINVAL
Comment out TrackDescription.Release until I can investigate API changes
Change Player.SetSubtitle's param
Fix bug with incorrect sizeof in Media.TrackInfo