AP_NavEKF: make use_compass() public
AP_AHRS: use EKF use_compass() if EKF enabled

this allows magfailed status to show on console via SYS_STATUS health
bits
Copter: make landing detector more strict

Made more strict by requiring 50 consecutive iterations where the climb
rate is below +- 40cm/s.  Previously it was 50 cumulative.

Removed check of failsafe.radio when clearing the land flag because it
could result in the vehicle taking off if the user picked it up.
Copter: remote arming check reference to compass learning
Copter: pre-arm check of internal vs ext compass
Mission: start next nav cmd immediately after prev completes
AC_WPNav: resolve twitch when passing spline waypoints

The target positions target velocity was being reset to zero as we
passed through a spline waypoint.
VRBRAIN: modified target clean
AP_HAL: added missing CONFIG_HAL_BOARD_SUBTYPE #define for HAL_BOARD_VRBRAIN
AP_HAL_VRBRAIN: added management for external relay 1 and 2
AP_relay: added default relay pin for VRBRAIN
VRBRAIN: added startup of internal mag's driver for VR Brain Standard 5
AP_HAL: VRBRAIN corrected EEPROM size and added terrain folder on MicroSD
AP_HAL_VRBRAIN: enable 2nd GPS for VRBRAIN 5
DataFlash: Added four more channels for logging
Copter: enable mount control with channels > 8 for radios with SBUS.
Build: VRBRAIN corrected order of MAG startup
Build: VRBRAIN corrected order of MAG startup for 4.5 board
AP_Compass: VRBRAIN. Deal with external mag connected on internal I2C on VRBRAIN 4.5
This enables user to set the external parameter to true even if only one compass is connected