Commit Briefs
use serial ids and drop usage of arc4random
it's not so useful here and not (directly) used anywhere else.
listener: correctly swap config after reload
and don't forget to free the current config!
fix the restart of the main process
delete useless functions such as merge_config and config_clear while here.
only memcpy into imsg->data if datalen is not zero
Passing a NULL pointer to memcpy is UB no matter if len is 0 (commit by claudio@, backporting for kamid.)