curator opens (too?) many files in upload-docs

[chreekat]

Reported by @juhp

Uploading docs to S3
Creating hoogle/orig.tar
curator: /home/curators/work/unpack-dir/.stack-work/install/x86_64-linux-tinfo6/d7d205a89b6867ea4451395ec473d03fcbc958590d23b15706959684c77259fd/9.8.2/doc/fits-parse-0.3.6/fits-parse.txt: openBinaryFile: resource exhausted (Too many open files)

I've addressed this in production by increasing the ulimit for the curators user. But it would be good to not use an unbounded number of open files eventually.