Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r241001: sigaction(2),sigwait(2),sigwaitinfo(2): Remove [EFAULT] error
condition.

Passing an invalid pointer results in undefined behaviour.

The wrappers in libthr access some of the data pointed to by the arguments
in userland, so that an invalid pointer will cause a signal and not an
[EFAULT] error return.

Furthermore, if the [EFAULT] error occurs when the kernel is writing, it is
not a proper error in the sense that the call still commits (changing the
signal disposition or accepting the signal).

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Clarify the behaviour of sigwait() on signal interruption, and note
the difference between sigwait() and sigtimedwait()/sigwaitinfo().

Approved by: re (bz)

Sort .Xr by section number.

Submitted by: ru

Add cross references to siginfo.3.

Fix up markup etc. in recently born manpage.

Insert missing copyright headers.

Fix plural.

Fix plural.

Add manuals for sigqueue, sigtimedwait, sigwaitinfo.