AC_WPNav: fix divide by zero when origin and dest are same location
GCS_MAVLink: Added message definitions for Rally Landing support.
GCS_MAVLink: Generated message code for Rally Landing support.
AP_Rally: More stateful.  Can now remember the last Rally Point chosen.
AP_TECS: added getter for flight stage.
AP_SpdHgtControl: Added FLIGHT_LAND_GO_AROUND FlightStage.
AP_Land:  A library supportingi landing from a Rally Point.
Plane:  Support for landing from a Rally Point added.