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).*
Let's remove this for now, can always add back later if requested.