Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use '%zd' printf format for ssize_t.

Check the return value of shutdown().

Add sigpipe, a simple UNIX domain socket and TCP regression test that is
intended to verify that SIGPIPE is delivered to a process writing or
sending on a socket that has been shut down for write. If available,
SO_NOSIGPIPE is also tested.

This regression test is currently passed by RELENG_4, but not by HEAD or
RELENG_5, due to a bug in the write() code for sockets. SO_NOSIGPIPE is not
present in RELENG_4, however, so is not tested there.

Reported by: Mikko Tyolajarvi <mbsd at pacbell dot net>
PR: 78478