Pawel,
If A/C units were a factory option, and if you could get hold of the data card, you could find out the answer to your question. However, since A/C was dealer-installed, I don't believe there's any way you could verify whether the car was originally sold with it. (Obviously, it would not have left the factory with it.)
I believe that A/C was less popular in Europe than in the US, and as you said, A/C and manual transmission may not be a common pairing. So, it feels less likely it was sold with A/C, but certainly not impossible. In any case, since A/C isn't a factory option anyway, having A/C now shouldn't affect the "originality" of the car either way (IMHO).
-David