Copter: reset battery_fs after dis/rearming
Copter: define limit for baro vs inav alt disparity
Copter: typo fix for baro vs inav alt disparity definition
AC_WPNav: add loiter_soften_for_landing method

This resets the position target to the current location.
Copter: soften loiter target when maybe landed

Applies to auto's land, land, loiter, pos hold and rtl flight modes
Copter: add land_complete_maybe flag
Copter: rename land_maybe_complete function
Copter: increase Alt Disparity check to 2m
LowPassFilter: add div by zero check
AC_PosControl: 2hz filter on accel error

Replaced hard-coded filter with LowPassFilter class allowing the
filter's to be 2hz on both APM and Pixhawk
AC_PosControl: 4hz filter on z-axis velocity error
Copter: use disparity threshold define for pre-arm checks

There are two duplicate checks, one in the pre-arm checks (i.e. checks
run every 15 seconds or so before the vehicle is armed) and one in the
arming checks (run immediately before arming).  The definition in the
pre-arm checks was still using the old hardcoded value.
Compass: always default devid to zero
AP_AHRS : Prevent EKF starting if GPS sats less than  AHRS_GPS_MINSATS
AP_NavEKF : Reduce weighting on GPS when not enough satellites

GPS measurement variance is doubled if only 5 satellites, and quadrupled if 4 or less.
The GPS glitch rejection thresholds remain the same
This will reduce the impact of GPS glitches on attitude.
Copter: allow passthru for ch 9 ~ 14

Based on work by Emile Castelnuovo
AP_NavEKF : Explicitly initialise gpsNoiseScaler to default value
Copter: update AC3.2-rc10 release notes
Copter: version to AC3.2-rc10
Copter: bugfix to condition-yaw for relative angles

Thanks to roque-canales for raising the issue and paradisephil for finding
the specific piece of code that went wrong and suggesting the fix.