xpi-extensions naming scheme

[Andrew Pantyukhin]

I urge contributors and committers to choose folder
names wisely for newly created xpi extensions. If
you take a look at [1] you'll find over a thousand
of extensions and two times that of undescores in
their names. Chances are we'll have dozens of xpi's
in our ports collection in just a few months. It would
be a shame if we were to see twice as much ugly
folder names.

If you absolutely like underscores, then go ahead
and use them. But I'd rather s/_// or s/_/-/ or even
use camel notation. Mozilla.org just chose this scheme
for storage, it doesn't really show up anywhere, while
in FreeBSD this is the primary way to address a
port.

Maybe it's worth it to rename adblock_plus and
pdf_download to something else - at maintainer's
discretion, of course.

PORTNAME/PKGNAME don't matter much, we can
change that later (in fact LATEST_LINK uses
${PORTNAME:S/_//g} at the moment).

Also, on a sidenote this whole xpi thing is not perfect
yet, and while we try to ensure that no changes to
the ports are required, it's a good idea to be prepared
to cooperate when we break something.

Thank you very much!

[1] ftp://ftp.mozilla.org/pub/mozilla.org/extensions/