[tlbuild] Asymptote 2.31

[Mojca Miklavec]

Hello everyone,

Asymptote 2.31 has been committed to the source tree. I'm not sure
about the status of other sources (whether any other patches are still
expected or if what's in SVN is final), but feel free to compile
asymptote any time from now. Hopefully that's the final version.

Please do the usual (commit the binary or send it to Karl).
    https://www.tug.org/texlive/build.html#asymptote
(I suspect that juggling with "mv .svn dot.svn" might no longer be
needed, but please don't take that for granted.)

Optional:
There have been a number of patches added in the last few days to
address various problems. As we kept struggling with "asy hanging
forever" a lot, I have a tiny request for those who are able and
willing to perform an additional test, just in case. If you have TeX
Live 2014 installed (collection latex-recommended is needed, most
probably nothing else), please try to do an additional "cd doc && rm
asymptote.pdf && make asymptote.pdf" after you build the ./asy binary
(just make sure that you don't commit the resulting pdf). This runs
asy on a bunch of example files, so if there are any major problems,
they might be caught during that test build already.

Known problems:
libc++ has a parsing bug that needs a special workaround, else asy
hangs forever. I'm not aware of libc++ being used on any platform for
which TL ships binaries (I'm aware that FreeBSD 10 and OS X 10.9 use
it, but we don't compile there), but if I'm wrong, please let us know.
(That workaround is only used on FreeBSD and OS X at the moment.)

Mojca