[Piglit] piglit-summary-html appears to have broken again

[Ilia Mirkin]

Dylan, do you have a minute to take a look?

~/src/piglit/piglit-summary-html.py -e skip -e pass tmp <(cat
nvc1-2015-04-28-ilia/results.json) <(xzcat nvcf-2015-07-05-mupuf.xz )
--overwrite
Warning: A python exception that should have been handled was not.
This is bug and should be reported.
BUG: [Errno 20] Not a directory: '/dev/fd/63'

Why is it expecting a directory? Should be able to just read the json
in... This definitely used to work...

  -ilia