RFC: root cert tool

[Juan Lang]

Since there wasn't a clear consensus about how to get CA certificates
into the registry, I decided to do what Mono does:  punt.  So I've
written a tool that can load certificates from a file or from a URL
and stick them in the registry.

By default it assumes you want to download them from Mozilla's CVS
front-end, and does so.

A patch that adds it is attached.  Comments?

Thanks,
--Juan