(ITS#8504) LDMB: Return EPIPE from mdb_env_copyfd2 instead abort on SIGPIPE

[lmb@cloudflare.com]

On 26 September 2016 at 20:48, Hallvard Breien Furuseth
<h.b.furuseth@usit.uio.no> wrote:
> I think we can skip sigwait() too since the thread will exit when done.
> Then any pending signals are presumably dropped.  (I suppose some OS
> could give them to another thread, but that goes against delivering
> them to a particular thread like SIGPIPE is.)

That's what my initial patch did. At least on OS X this leads to the
process receiving SIGPIPE and dying. I can attach a test case as well
if desired.