reside, and move there ipfw(4) and pf(4).

o Move most modified parts of pf out of contrib.

Actual movements:

sys/contrib/pf/net/*.c		-> sys/netpfil/pf/
sys/contrib/pf/net/*.h		-> sys/net/
contrib/pf/pfctl/*.c		-> sbin/pfctl
contrib/pf/pfctl/*.h		-> sbin/pfctl
contrib/pf/pfctl/pfctl.8	-> sbin/pfctl
contrib/pf/pfctl/*.4		-> share/man/man4
contrib/pf/pfctl/*.5		-> share/man/man5

sys/netinet/ipfw		-> sys/netpfil/ipfw

The arguable movement is pf/net/*.h -> sys/net. There are
future plans to refactor pf includes, so I decided not to
break things twice.

Not modified bits of pf left in contrib: authpf, ftp-proxy,
tftp-proxy, pflogd.

The ipfw(4) movement is planned to be merged to stable/9,
to make head and stable match.

Discussed with:		bz, luigi