Torouter on Buffalo breaks with large cached-descriptors[.new] files

Torouter breaks with 64MB flash memory because of large cached-descriptors[.new] files. Jake reports that he tried to start a bridge with these files being 12M and 9M large, which made his box die badly.

The question is whether we can throw out cached descriptors more quickly on a bridge. Which leads to the question whether bridge clients request descriptors from us, or if they only establish a directory connection to a directory mirror via us.