AP_Math: fixed build warning
RC_Channel: added set_radio_trimmed()

take into account trim value in set_radio()
Plane: use set_radio_trimmed() for flaperons

See discussion in issue #1425
GCS_Mavlink: New message def: MAV_CMD_NAV_CONTINUE_AND_CHANGE_ALT
GCS_MAVLink: include units in CONTINUE_AND_CHANGE_ALT
GCS_MAVLink: code generation from XML for MAV_CMD_CONTINUE_AND_CHANGE_ALT.
AP_Mission: support for MAV_CMD_CONTINUE_AND_CHANGE_ALT
Plane: Implementation of MAV_CMD_CONTINUE_AND_CHANGE_ALT.
Plane: Keep throwing WP in front plane for CONTINUE_AND_CHANGE_ALT
Plane: fixed CONTINUE_AND_CHANGE_ALT command

current_loc should be used, not prev_WP_loc
AP_Mission: Support MAV_CMD_DO_FENCE_ENABLE as a mission item.
Plane: Support MAV_CMD_DO_FENCE_ENABLE as a mission item.
Plane: fixed missing break statement
AP_Math: fixed example build
Plane: prepare for 3.2.0 release
AP_HAL_Linux: Add support for in-kernel SPI CS handling

Add support for /dev/spidev<bus>.<cs> in-kernel SPI CS handling, and convert
existing SPI devices over.

 * Add a new member _subdev to the LinuxSPIDeviceDriver class, and initialiser
   in LinuxSPIDevice constructor.  Use subdev 0 for GPIO-managed CS
 * Extend the _cs_pin to signed 16 bits and define SPI_CS_KERNEL (-1) for
   kernel-managed CS
 * Move to per-device file descriptors (required for in-kernel CS)
 * Extend spidev filenames to include bus and subdevice numbers, possibly
   longer than 1 digit each
 * Allow support for platforms enumerating /dev/spidevNNN from non-zero bases
 * Convert existing users over to the new API

Signed-off-by: John Williams <john@whelanwilliams.net>
HAL_Linux: tidy up SPI debugging a bit
build: added motor_test, and fixed build checks for PX4
PX4: disable auth command to keep us below 1MByte
AP_HAL: added set_esc_scaling() RCOutput function

this will be used to scale outputs for uavcan ESCs based on throttle
range