Well, originally I had thought about using bools. That is why some comments/docs refer to things as true and false. However, in the middle of the process I decided against it because we might find non C99 compilers out there.
Our configure.ac will do the magic and define bool for those compilers but given that cf-upgrade needs to be completely independent from our code, I found it better to fall back to ints.
I'm not particularly picky about this, so I can switch to bools and include <stdbool.h> if that is prefered.