[tlbuild] asy2.49 build

[Karl Berry]

I updated the asy runtime files with 2.49
(and the x86_64-darwin binary, thanks Dick),
although the usefulness of TL continuing to distribute any asy binaries
remains unclear to me.

At any rate, I think we are just about ready to start the final push
toward the release ... except for asy. If you can't build a useful
binary, I suggest just dropping it. I don't much care for the idea of
indefinite delay while all these OpenGL portability problems are batted
around. --best, karl.