Only upload addons from Linux; also ignore a few mac specific files.

Until/unless we ever end up with binary addons, we should just use the ones built on Linux...even though they should all in theory be identical, I don't trust the ones built on Mac or Windows as much not to break, especially since both Mac and Windows tend to lag behind in terms of development and in regard to their xulrunner versions.

I'd also suggest we maybe get something setup to coordinate the buildbots via a server, and build into the script the ability to determine if the machine the script is running on is supposed to build anything more than the client itself in later versions.

GeekShadow: I cleaned up the comments a bit too, but you may want to remove the space on line 1 if you merge this...and remove any double space comment situations I created.