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

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

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

Approved by: re (implicit)

o style.Makefile(5): WARNS= -> WARNS?=.

Add a regression test for listen()'s backlog argument, both at time of
creation and at time of update using an additional call to listen().
This test also exercises SO_LISTENQLIMIT, a forthcoming socket option
that allows the retrieval (but not setting) of the queue limit.

Discussed with: andre