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).*
I couldn't quite get the ` inreplace ` to apply cleanly. I've added a comment to the upstream issue asking for clarification on the status of this. It'd be nice if they removed that chunk of code, given Misty's explanation a year ago as to why it isn't necessary any more.