Copter: make CIRCLE_RATE a tunable parameter

Also bug fix to check of how many time it has rotated during a loiter
turns mission command
AP_AHRS: made a few methods const
AP_Param: make it easier to show the value of a parameter
AP_GPS: make status() const
AP_Common: added a define for PACKED

neater than a pragma
AP_InertialSensor: make some interfaces const
DataFlash: new dataflash logging system

this allows us to remove the display functions in the vehicle code,
and also allows us to store the format of a log file in the log. It
also stores the parameters used in a flight, rather than the
parameters set at the time the log is dumped
Rover: convert to new logging system
Plane: make the plane code compatible with the new logging system

not actually converted yet
Copter: make copter code compatible with the new logging system

not fully converted yet
VARTest: fixes for new logging system
DataFlash: dump the format of logs at the start of the log
Rover: use new StartNewLog() interface
Plane: convert to new logging system
Rover: added compass logging
Plane: added compass logging
Plane: when logging is disabled don't include DataFlash at all
Rover: cleanup build warnings
AP_Math: move print_latlon() to location.cpp
DataFlash: use print_latlon()