Copter: GCS_mavlink only send waypoints to gcs3 if initialised

Also Load parameter defaults at initialisation (although defaults are
all zero anyway so should have no effect)
Plane: fix to gps present check in mavlink extended status 1 msg
Copter: fix to gps present check in mavlink extended status 1 msg
INS: relax accel offset check to 3.5 m/s/s

One user, Dusty, has found that even with offsets of 3.1 m/s/s
successful alt hold and loiter are possible
Plane: unlock roll and pitch when we enter ACRO mode
AP_AHRS: fixed spin rate gain conversion from degrees to radians

fixes issue #433

Thanks Jurgen!
RC_Channel: fixed dead_zone for range channels

The dead_zone was being used inconsistently, used in PWM space in one
place, and in control output space in another.

The fix required us to move the index number of the RC channel eeprom
value for RCn_DZ, as users will have a throttle deadzone of 3 set in
their eeprom due to a bug that Randy just fixed that caused the value
to always be saved to eeprom. In plane we then need to fix the
deadzone for the throttle to be 30

this fixes issue #303

Thanks to Soren Kuula for spotting this!
Plane: fixed default deadzone for the throttle channel

this is the 2nd half of the fix for issue #303
Copter: thr failsafe will not RTL if in batt failsafe

resolves issue #413
Copter: pre-arm check of throttle failsafe value

Check throttle min is above throttle failsafe trigger and that trigger
is above ppm encoder's loss-of-signal value of 900
Plane: added a new CRUISE flight mode

See
http://diydrones.com/group/apmusergroup/forum/topics/feature-request-hold-heading-mode

this fixes issue #438
AP_AHRS: removed get_roll_rate_earth() and get_pitch_rate_earth()

these are not used any more
APM_Control: changed attitude controllers to take angular error not angle

this makes it easier for ACRO mode
Plane: update for new APM_Control API
Plane: re-do roll hanging in ACRO mode

this avoids the euler angle zeros of the previous method by using a
gyro integrator on the roll axis

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
Plane: change to 2.73beta4
AP_Airspeed: added get_airspeed_ratio() and set_airspeed_ratio()

This is to help Paul develop an automatic tuning system for airspeed
ratio
Copter: pre-arm checks for rc ch 1~4 min and max
GCS_MAVLink: merge in latest upstream XML changes
GCS_MAVLink: merge in changes from upstream mavlink repo