Adding breakByteEnd to mirror breakByte

I have written a simple alternate version of of `breakByte`, called `breakByteEnd` which uses `elemIndexEnd` instead of `elemIndex`, as well as rewrite rules for `breakEnd` to mirror those of `break`. This is merely in the interest of completeness in library functionality, and is not per-se a critical addition.
Have you tried what happens if we don't comment these tests out? I'd rather actually add the tests than add commented out versions :-)