[Shtoom] upnp leaking mappings

[Zooko O'Whielacronx]

Whenever I do UPnP, I see a list of "existing mappings" which is one 
greater than the last time I did UPnP.

Also the most recent time I did it my linksys didn't respond to the 
upnp discovery broadcast at all until I disabled and re-enabled upnp in 
the linksys admin web page.

I had assumed that these mappings would time-out if they weren't 
refreshed, but they've lived for days now.

Ought they to be cleaned up, and if so how?

--Z