[tlbuild] TL rebuild for asy 2.26, other engine fixes

[Karl Berry]

John B has released asymptote 2.26.  I've updated the sources in TL,
and committed the support files and i386-linux and windows binaries.
Please rebuild it for your platform, if relevant.

Also, there have been a few small fixes to other programs, so please
rebuild everything and email|commit as usual.  Be sure to get the
current sources, I committed a xetex fix just a few minutes ago (r33705).

Thanks,
Karl