[tex-live] installing pretest in cygwin 64: install-tl and tlmgr errors.

[Karl Berry]

    it fails (shouldn't @INC have
    /usr/local/texlive/2016/texmf-dist/scripts not /texmf-dist/scripts ?

Indeed.  (It's because it couldn't determine `dirname $0`, essentially.
We should probably abort earlier when that fails.)

    /usr/local/texlive/2016/bin/x86_64-cygwin/fmtutil: kpsewhich
    -var-value=TEXMFROOT failed, aborting early.

I believe some of the cygwin dll's are missing from the build at the
moment.  I'll fix what I can see for tonight.

Thanks for the report,
Karl