Right now there's a single warn_if_unnamed flag for
router_get_consensus_status_by_nickname() and
node_get_by_nickname(), that is nearly always 1.  I've turned it
into an 'unsigned' bitfield, and inverted its sense.  I've added the
flags argument to node_get_by_hex_id() too, though it does nothing
there right now.

I've removed the router_get_consensus_status_by_nickname() function,
since it was only used in once place.

This patch changes the warning behavior of GETINFO ns/name/<name>,
since all other name lookups from the controller currently warn.

Later I'm going to add more flags, for ed25519 support.