change old running scripts with rcNG

[Thomas-Martin Seck]

* Sergey Matveychuk (sem at ciam.ru):

> I've found rcNG-style scripts very convenient. I just set 
> servicename_enable="YES" and port specific variable as 
> servicename_opt="..." and I have not to rename 
> PREFIX/etc/rc.d/script.sh-dist or like that.
> 
> What maintainers think to move to rcNG style scripts?
> You can take a look at mail/p5-Mail-SpamAssassin port as an example.

Starting with 2.5.4_6 the squid ports installs a squid.sh that will work
like an rcNG script when either /etc/rc_subr or $PREFIX/etc/rc_subr are
present. If not, it will behave the "classic" way.