[tlbuild] asymptote build

[John Bowman]

> It would be still preferable if everything could be contained within
> TL directory structure. One of the reasons is portable use from USB

I agree that is reasonable also outside of cygwin, for the TL distribution.

Isn't there already a HOME variable we can use or do you really need
a new environment variable called ASYHOME.

'kpsewhich --var-value=ASYHOME'

The ASY qualifier doesn't make sense to me as this should have nothing to
do with ASY per se. Any project looking for a home directory will have this
probblem. I suggest using kpsewhich to look up HOME and then adding on the
hard-wired suffix ".asy" for consistency with the other asy distributions.

-- John