(Membership Information): Renamed the reserved1 bit of Membership-Type
to passive-message-invert. Document it. (async-send-message): Mention that the passive and passive-message-invert bits of the Membership-Type influences if messages are sent or not. (send-message): Mention passive and passive-message-invert. Mention async-send-message. (Error Codes): Don't say "group message".