a connection's timeout is halved for every extra connection
from the same host.
Also keep track of when we don't need to use a connection
anymore, so we can close it and free the resource for another
connection.
Also use the longer timeout for non routable local addresses.
The commands handler must not be destroyed before the config
object, or we'll be accessing freed memory.
An earlier attempt at using boost::shared_ptr to control object
lifetime turned out to be very invasive, though would be a
better solution in theory.
