bug#8565: gzip/bzip2/output-hook support for split

[Ari Pollak]

I've been sitting on this for a few months expecting to finish it, but
still haven't found the time, so I'm just putting it out there now so
it isn't lost entirely. It's originally from Chandrakumar Muthaiah:
http://article.gmane.org/gmane.comp.gnu.coreutils.bugs/15684
I applied it to the latest git, added some tests, and cleaned it up a bit.

output-hook.diff
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