AC_WPNav: use atan2f, make methods const
Mission: make get_prev_nav_cmd_index const
AP_Mission: fixed a bug re-entering AUTO

this fixes a bug found by Marco where we would continue in CRUISE mode
with no waypoint if we re-entered AUTO after a mission reset
Rover: added BRAKING_PERCENT parameter

this allows for reverse throttle to be applied for braking in corners
Copter: add drift throttle assist
Copter: Drift throttle assist range increased

Throttle assist is applied from 213 ~ 787
Deadband and constraint added
Copter: add Drift throttle assist constraints
Rover: make log_bitmask 32 bit

this fixes the log before arm
AntennaTracker: fixed mode set using custom mode
AntennaTracker: fixed pitch slew rate limit
Copter: Only play GPS tone when armed
Copter: Remove 80m altitude limit on RTL
Copter: remove do_land's use of RTL_ALT_MAX
AP_Notify: correct dos formatting
Notify: add arming failure tone
Copter: integrate Notify arming failure when using yaw sticks
Copter: Notify arming failure when using MAVLink
Copter: disambiguate the various causes of "Bad GPS Pos"

I've seen a fair number of user questions where they are confused by
"Bad GPS Pos" on their GCS/not being allowed to arm.  This change splits
the remaining causes of this fault into separate messages.

Hopefully this increases the odds of the user self diagnosing...
AP_NavEKF : Improved GPS glitch detection

This adds new functionality to the detection and compensation of GPS
glitches:

1) The filters own innovation variance estimate is scaled to calculate
the maximum allowable GPS position innovation
2) If the innovation length exceeds the maximum allowable, no fusion occurs
3) If no fusion has occurred for long enough such that the position uncertainty
exceeds the maximum set by a per vehicle parameter or a maximum time, an offset
is applied to the GPS data to so that it matches the value predicted by the filter
5) The offset is never allowed to be bigger than 100m
6) The offset is decayed to zero at a rate of 1.0 m/s to allow GPS jumps to
be accommodated gradually
7) The default velocity innovation gate has been tightened up for copter and rover