PX4: change FMUv2 bootloader USB ID to 0x0011
PX4: added automatic IO firmware update

this avoids the px4io.loaded file on the SD card that confused many
users
AP_InertialSensor: prevent INS healthy errors while initialising

during gyro cal we shouldn't mark the gyro unhealthy
AC_WPNav: reduce leash length for stopping

We now limit the target stopping point to 1x the xy leash length while
previously it was 2x.  This is justified because this limit is only used
when the copter is travelling at higher speeds but at higher speeds air
drag tends to make the copter stop more quickly naturally.