po: Add and fix a few Finnish translations.

[Lauri Kenttä]

"Thai" is right, "Thain" is wrong. Please don't mess with Finnish if 
you don't know it. As I've said, I'm working on it. If you feel I'm too 
slow, feel free to hire me and I'll do it faster. ;)

I'm currently away from my computer, but I'll send my patch this 
weekend. It will have almost everything except some of the more 
difficult winerror and crypt* texts.

-- 
Lauri Kenttä