[Xastir] Support for PHGR

[Eric Christensen]

While doing research on my previous question I ran across this document
(http://eng.usna.navy.mil/~bruninga/aprs/probes.txt) in reference to
PHGR which adds a figure on the end of the PHG statement to represent
the number of times it transmits its' position data ever hour.  This was
put in the APRS Spec Erratta
(http://eng.usna.navy.mil/~bruninga/aprs/errata.html).

Eric