apr 1.5.1 (new formula)

New formulae for apr, apr-util and a reworded/repurposed requirement to fit both. The existing syntax in-formulae of ` depends_on :apr ` doesn't need changing, It should and appears to work as is. *(Which is nice, usually when I expect something to work as is it doesn't).*
Cool. You and the other maintainers all have access these days, so you can make changes as desired if I can't or I'm offline for a while or whatever.