pkg_verify 0.1 is released. This is a tool to verify installed official Slackware packages. I’ve thought of writing something to parse the MANIFESTs and do the comparisons for a long time, but I am only just now actually doing it. It’s the sort of tool one doesn’t need very often, but when one does, it can be highly useful indeed.
Take a look at the pkg_verify page for the requisite info.