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).*
Interestingly, If ` apr ` builds first, which it should do as it's a dep here, and ` apr ` is built with ` ENV.deparallelize `, this builds fine without ` ENV.deparallelize `. I'll push to the bot and let it double check I'm not just getting lucky.