make 'proxy-hosts' into a list?

Folks, I'm doing a little to handle hosts that are down a
bit better.

Previously, you had to change your ARK host <status>
(i.e. in the XML file) to 'inactive', but that's just too
uncool, and also unwieldy for a site of any size.

I'm adding a command-line flag (which, as with any flag, you
can "permanently" set in your ARK_PROFILE file)
--down-hosts=... and anything you try to do on those hosts
(actually run things) will be marked as "deferred".

But how about another keep-the-show-on-the-road-thing?
Instead of having just one proxy-host per proto-host (see
package/ALL.xml for any site), e.g.

   <proxy-hosts><table>
     <entry name="ALL">slicker</entry>
     <entry name="ia32-linux-rh7.1">gorregan</entry>
     <entry name="sparcv9-solaris2.6">slinger</entry>
   </table></proxy-hosts>

we instead make the entries be lists, and the proxying gig
will check them in order until it finds a non-down one? e.g

   <proxy-hosts><table>
     <entry name="ALL"><list>
	<item>slicker</item>
     </list></entry>
     ... etc ...
   </table></proxy-hosts>

Please yell back "No!" if this adds useless complexity...

Will