Bundle of random changes

Hi Heinz, many of the changes in this branch are unrelated to each other, so you can cherry-pick the ones you want. 

--exclude-from is an idea for implementing a whitelist for specific Slackware packages, there is a separate commit for an example whitelist file.

I'm not sure that I like the suggested architecture check changes. If you don't like them, that's ok :-) but if you do like them I'll add some more sub-checks to make it more useful.