[tlbuild] Asymptote and Python3

[Mojca Miklavec]

Hi,

For the last few years we have been going through hectic testing &
patching of Asymptote in the last moment before the freeze of TL
sources.

I would love to see Asymptote support Python 3 and I submitted a long
patch, but there are still some problems. See:
    https://github.com/vectorgraphics/asymptote/tree/python3

(xasy from MacTeX 2015 fails to work for me unless I explicitly start
it with python2 because I had to switch to python3 as my default
Python interpreter.)

I would be grateful if any of you would be willing to test and
contribute patches now, so that we could end up with a functional
support for Python 3 in time for TL 2016.

Thank you,
    Mojca