[ntp:questions] Nasty PPM change by 4.2.7

[A C]

Version 4.2.7p270 just did a very nasty thing when I took away its 
preferred clock and allowed the reach counter to hit zero (the preferred 
clock is GPS).  It set the clock PPM to 'nan', wrote that into the drift 
file and then let the clock spin out of control.

I was working on the GPS and had to turn it off for a few minutes.  The 
system has several other Internet servers configured but for some reason 
it just blew up instead of dropping the clock and moving to another.

This is unrelated to the overflow that happened earlier.  I caused this 
one by turning off the GPS but it still shouldn't have plugged 'nan' 
into the PPM control.