Fixed handling the [Abort] button in installer (inst_user_first)

- Uses are now asked to confirm that they really really want to Abort
- bnc#886662
- I've also fixed UsersSimple.Transliterate not to return a trailing newline
Then I would need to take care about creating new library as modules are written in Perl. And I'd need to take care about proper packaging. This is tested manually now and while I usually write tests, I've decided not to do it this time.