[tlbuild] general rebuild + asy 2.38

[Karl Berry]

I'm sorry, but we will need to rebuild one more time (no plans for more,
but then there were no plans for this one, so what do I know).

There are fixes to luatex, xetex and dvipdfmx, and a new version of pmx.
(The LuaTeX change is the only one that's really crucial.) 

There is also a new version of asy, 2.38, with a couple of bug fixes.
Its TL source (Build/utils/asymptote) is updated, and I committed the
support files and i386-linux binary for the new version.

Thanks/sorry,
karl