bug#9089: pipe failure with cat and head of coreutils 6.12

[Paul Eggert]

Assaf Gordon wrote:
> If the issue of cat(1) supporting socketpair/ECONNRESET instead of
> pipes/EPIPE is still relevant, we can re-open the bug.

'cat' treats EPIPE on pipes the same way it treats ECONNRESET on socket pairs:

$ (trap '' PIPE; cat /usr/bin/emacs) | :
cat: write error: Broken pipe

The difference in observed behavior occurs only because most scripts (rightly) 
don't ignore SIGPIPE. If we change 'cat' to ignore ECONNRESET, for consistency 
we should also change it to ignore EPIPE.

The POSIX spec[1] allows 'write' to send a SIGPIPE and set errno to EPIPE for 
sockets that are no longer connected. I wonder why the Linux kernel doesn't do 
that? It would seem to be more consistent and useful.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html