This allows a big swath of ifdefs to be removed. It also means savings as the db var is not passed around all of the time, and makes it easier to remove the final broker call to mosquitto_time() call in packet_mosq.c. In one test this reduced the calls to mosquitto_time() from 295k to 48k.
This is not specific to authentication, and allows plugins greater flexibility in what events they are interested in. It also adds message handling, and $CONTROL handling.
