Re: condoms to prevent disease within marriage
The Church has pretty much ruled that using condoms during sex is never licit, but it wouldn't be because of the procreative aspect of sex but because of the unitive aspect. Using a condom during intercourse prevents sperm from being deposited in the vagina which is an essential part of the act according to the natural law theory advanced by the catholic church.
Now using a condom is certainly less serious than infecting your spouse with HIV but I can't imagine the church ever encouraging people to do the lesser of two evils. If the pope really thought that using condoms in Africa would stop the spread of AIDS the only moral thing for him to do would be to say nothing at all.