[tlu] beta with support for TL 2016

[Adam R. Maxwell]

I've just uploaded a new beta with support for the SHA-512
hash check introduced for TeX Live 2016 pretest. If you're
using the pretest, please give it a try.

https://github.com/amaxwell/tlutility/releases/download/1.24b3/TeX.Live.Utility.app-1.24b3.tar.gz

Note: as of now, update-tlmgr-latest.sh does not actually
seem to update anything (I get the same version numbers
after running it). At least it downloads, though.

In theory, this will also work with TL 2015 and earlier,
but I haven't yet tested it there.

-- adam