This can't actually result in a null pointer dereference, since
pub_excl and sub_excl are only set when the corresponding smartlists
are nonempty. But coverity isn't smart enough to figure that out,
and we shouldn't really be depending on it.
Bug 29938; CID 1444257. Bug not in any released Tor.
Having the numbers in those messages makes some of the unit test
unstable, by causing them to depend on the initialization order of
the naming objects.
This code tries to prevent a large number of possible errors by
enforcing different restrictions on the messages that different
modules publish and subscribe to.
Some of these rules are probably too strict, and some too lax: we
should feel free to change them as needed as we move forward and
learn more.
