Bug: deadlock from msyslog

[Hal Murray]

A while (months) ago, we had troubles with msyslog scrambling output when 
called from the DNS thread and the main thread at the same time.  That was 
fixed by adding a lock.

That will deadlock if a signal handler calls msyslog when the signal goes off 
in the middle of a msyslog call.

I poked around a bit.  There are a few signal handlers that call msyslog.  I 
think they can be deferred.  It's probably worthwhile to study all the signal 
usage and make some notes.

The only timing critical signal handler that I know about would be the one 
grabbing the time of received packets.  That code doesn't get enabled by our 
current build system.  NTP Classic uses it on NetBSD.

-- 
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