Avoid mirroring a distfile

[Andrea D'Amore]

Due to recent discussion on Virtualbox [1] I replaced my binary with
Macports provided application, in doing so I needed the VirtualBox
Extpack for handling USB 2.0 in host OS.
I'd like to add a port for this extension, say virtualbox-extpack,
depending on virtualbox port. Checking the license [2] and relative
FAQ I see point 7. at [3]

"Can I redistribute the VirtualBox binaries?
No. The Personal Use and Evaluation License allows you to download the
VirtualBox binaries for personal and academic use and for evaluation,
but it does not give you the right to redistribute these binaries."

Since the extpack come as binary this means that it cannot be mirrored
on Macports distfiles folder and its mirrors.

I never digged into the mirroring thing, is a distfile mirrored
automatically or by hand?
Can portfile specify some keyword against this?


-- 
Andrea

[1] http://lists.macosforge.org/pipermail/macports-users/2012-January/027181.html
[2] https://www.virtualbox.org/wiki/VirtualBox_PUEL
[3] https://www.virtualbox.org/wiki/Licensing_FAQ