Copter: increase EKF_CHECK_THRESH default to 0.8

Also remove unused #define related to inertial nav check (now removed)
Copter: reduce alt hold defaults

Throttle Rate P to 5.0 (was 6.0)
Throttle Accel P to 0.5 (was 0.75)
Throttle Accel I to 1.0 (was 1.5)
TradHeli: update AttControl params to match multicopters
DataFlash: allow use of a smaller writebuf for PX4v1

this fixes logging on PX4v1
Copter: send extended status to GCS only after initialisation
Copter: never send unhealthy terrain status

Copter does not yet rely on the terrain data (it's for informational
purposes only) so we will temporarily disable the failure flags to the
GCS to avoid support calls
AP_NavEKF : Clean up time stamps

Time stamps are now explicitly initialised to the current IMU time to avoid unwanted activation of timeout logic on filter start and various calls to the hal.scheduler->millis() object have been consolidated.
AP_NavEKF : Reduce ripple in estimates that can cause copter motor 'pulsing'

This patch reduces the level of 5Hz and 10Hz 'pulsing' heard in motors due to GPS and altimeter fusion which cause a small 5Hz and 10Hz ripple on the output under some conditions. Attitude, velocity and position state corrections from GPS, altimeter and magnetometer measurements are applied incrementally in the interval from receiving the measurement to the predicted time of receipt of the next measurement. Averaging of attitude state corrections is not performed during periods of rapid rotation.
Copter: AC3.2-rc8 release notes
Copter: version to AC3.2-rc8
HAL_PX4: fixed dirty_mask calculation in FRAM storage

this could lead to a number of bytes on 512 byte boundaries not being
written when changed in ram, so they would revert on next boot
HAL_VRBRAIN: fixed storage bug in VRBRAIN too
Copter: AC3.2-rc9 release notes
Copter: version to AC3.2-rc9
VRBRAIN: modified target clean
DataFlash: Added four more channels for logging
Copter: enable mount control with channels > 8 for radios with SBUS.
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
VRBRAIN: defined AirSpeed inputs for ArduPlane on VR Micro Brain 5
VRBRAIN: added flag for to build versions with different kind of RC Inputs