Hi, I am posting this just to help anyone who installed the latest Slackwarearm-current, of July, 2018, and didn't get the Pi camera to work. I googled and searched to no avail, until I found this website: https://hup.hu/node/142356. It contains a script with all the steps necessary to make the Pi camera work. You can either follow the script steps manually, or carefully edit it to run as sh script, then run it as root.
Be warned there is a small error in the <<EOF notation, which should be just an EOF, but it is easily fixed to run right.

The script basically builds the Raspian "userland" programs, setups the correct video group, sets a udev rule, and adds the userland programs to the $PATH. It also shows what needs to be added to /boot/config.txt to enable the camera.

I'm very grateful to the author for posting this solution, and I think it should be included in the sarpi extra scripts, since so many people want to use the Pi camera.
Otherwise, the latest Slackware-arm-current runs great on my Raspberry Pi. Good luck!