Bayeux Advise implementation.
See http://svn.xantus.org/shortbus/trunk/bayeux/protocol.txt for the technical
details.
The advice system provides a way for servers to inform clients of their
preferred mode of client operation. In conjunction with server-enforced limits,
Bayeux implementations can prevent resource exhaustion and inelegant failure in
several important edge cases. Since transport evenlopes are "pluggable" in
order to support differing "on the wire" behaviors, advice values may also vary
by transport type, even for the same conditions. What follows is a breif
description of the enumerations that are used in advices and their canonical
meanings.