autotest: fixed valgrind options to sim_arduplane.sh
PX4: make compass calibrate fail non-fatal

until we sort out what is going on with compass calibration failures
this is the best option
GCS_MAVLink: allow for proxying of larger MAVLink messages on PX4

this makes it possible to deal with large MAVLink messages
DataFlash: return number of logs as zero correctly 

when we have no file based logs, report no logs :)
GCS_MAVLink: send a "zero logs" message when no logs available
autotest: fixed multi-instance support
autotest: initial version of a antenna tracker simulator
autotest: added -T option to sim_arduplane.sh

starts an antenna tracker
AntennaTracker: fixes for antenna tracker

- use pressure to calculate vehicle altitude
- changed approach to slewing
- fixed mavlink mode
AntennaTracker: added a note on simulating an antenna tracker
AntennaTracker: added sending on SIMSTATE in SITL
autotest: raise turn rate of antennas
autotest: kill off old tasks on exit
Rover: fixed comment
Plane: print PX4 compass type
AP_Compass: fixed showing of is_external for 2nd compass