[tlbuild] Installation with new binaries

[Karl Berry]

    Error: `mpost -ini  -jobname=metafun -progname=mpost metafun.mp' failed
    fmtutil: running `pdftex -ini   -jobname=cslatex -progname=cslatex -etex 
    -translate-file=cp227.tcx cslatex.ini' ...

In general, it would be helpful to see the actual error messages from
mpost.

But I think the answer is yes, expected, since I just started this
morning to put together the pretest hierarchy, fmtutil.cnf is not yet
updated as needed for the new mpost.  I hope to do that later today/this
weekend.

(And furthermore, once fmtutil.cnf is updated, binaries on platforms
that have *not* been updated will fail.)

Thanks,
k