s3: forward MSG_DEBUG from smbd parent to all children

s3: forward MSG_DEBUG from smbd parent to all children

Before 3.3, an smbcontrol debug message sent to the target "smbd" would
actually be sent to all running processes including nmbd and winbindd.
This behavior was changed in 3.3 so that the "smbd" target would only
send a message to the process found in smbd.pid, while the "all" target
would send a message to all processes.

The ability to set the debug level of all processes within a single
daemon, without specifying each pid is quite useful.  This was implemented
in winbindd in 065760ed.  This patch does the same thing for smbd.

Upon receiving a MSG_DEBUG the parent smbd will rebroadcast it to all of
its children.

The printing process has been added to the list of smbd child processes,
and we now always track the number of smbd children regardless of the
"max smbd processes" setting.