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

Because POSIX does not allow EINTR to be returned from sigwait(),
add a wrapper for it in libc and rework the code in libthr, the
system call still can return EINTR, we keep this feature.

Discussed on: thread
Reviewed by: jilles