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)

Some code cleanups, including removing of stale getopt argument and
hardcoded +CONTENTS defines.

PR: bin/117855
Submitted by: Beat Gaetzi <beat@chruetertee.ch>
MFC after: 14 days

Introduce pkg_updating(1) which scans for installed ports and shows
all ports/UPDATING entries that affect one of the installed ports,
and are relevant on the given machine.

PR: bin/117564
Submitted by: Beat Gaetzi <beat@chruetertee.ch>
MFC after: 14 days