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)

Style: NO_MAN doesn't need any value.

Use WARNS?= instead of WARNS= in Makefiles so that global warning
settings can override local ones.

Pointed out by: ru

Add test which excersises problem with unability to change association of
already associated datagram unix domain socket by issuing connect() system
call.