added osc_locked sensor
added health getter
bugfixes and indents
added advanced gpsdo sensors

Added functionality:
* gps_osc_locked: checks for the SYNC:LOCKED? status
* gps_osc_health: returns the status hex string
For reference, refer to
http://www.jackson-labs.com/assets/uploads/main/firefly_1A_manual.pdf,
page 13 (PDF page 19)

	host/lib/usrp/gps_ctrl.cpp
Merge branch 'master' of git://code.ettus.com/ettus/uhd
fixup