[OS X TeX] Adding TL'21 (pretest) to TeX Live Utility/texbin

[Joseph Wright]

Hello all,

The TL'21 pretest has begun, so I've installed it on my Mac using the 
generic Unix installer (sudo install-tl -repository <a-pretest-server>). 
It's been a few years since I last did this on a Mac, and I don't 
remember how to set up the /Library/TeX/texbin business to find TL'21. I 
guess I also need to 'tell' the TeX Live Utility GUI about it.

Anyone know the 'recipe'?

Joseph