[LinuxPPS] another refclock_nmea patch ([Bug 610] Generic NMEA GPS Receiver driver w/ PPS expects PPS after NMEA data)

[Udo van den Heuvel]

https://support.ntp.org/bugs/show_bug.cgi?id=610

The NMEA patch appears to be accepted.
Now some small documentation changes needed?

BTW: is pps (atom) driver not opening the device a feature?