New portmaster with -o and other fixes

[Craig Boston]

>   Log:
> 
>   New Feature
>   ===========
>   --clean-distfiles[-all] options to check /usr/ports/distfiles for
>   stale stuff, and either offer to delete them or delete them all
>   without prompting.

That's excellent news!  Now I can use -D during upgrades to avoid
pausing between port builds, and run this later to manually clean up the
distfiles.

I'm a bit paranoid about automatically deleting them -- had one too many
times when port[master|upgrade|foo] got confused by slave ports or weird
file names and deleted hard to replace* distfiles.

(* Stuff like the openoffice source that is huge, or java source that you
have to fetch manually)

Thanks again for your work on portmaster!

Craig