Bugzilla - Add keyword and remove OS's

[Dan Kegel]

Austin wrote:
> The OS list in bugzilla is a bit excessive. There are 16 OS's that I
> think we should remove...

I think we should keep most of them, but classic Mac OS
(pre-X) can go, as we never worked there (not even Darwine),
and nobody cares about it anymore.  I've deleted
Mac System 7, and will delete the rest of the classic
mac OS's if there is consensus.