AP_Motors: Added MOT_UNSAFE_THR parameter - Throttle setting used to signal that the copter is armed or otherwise unsafe to approach
Copter: Warn user with motors while copter is arming
Copter: Cancel arming if throttle input above cruise_throttle.
Copter: do not spin motors during arming process
Copter: renamed MOT_UNSAFE_THR to MOT_SPIN_ARMED

Removed special purpose spin_unsafe function
renamed _throttle_unsafe to _spin_when_armed and changed to an AP_Int8
Copter: implement safety spin for Tricopters
Copter: fix to SPIN_ARMED parameter desciption
Copter: ensure _spin_when_armed is not higher than _min_throttle
Copter: ensure take-off alt is at least 1m

fixes issue #377
AutoTest: rename and remove copter mission files
Copter: initialise ch7 and ch8 aux switches

This ensures that if you have simple mode or sonar attached to an
auxiliary switch it will be enabled or disabled according to the switch
immediately after start-up
APM_Control: allow for a wider range of P values for roll/pitch

values above 1.0 are sometimes needed
AP_SpdHgtControl: rename flybywire_airspeed to airspeed

this variable applies to any automatic throttle mode, not just FBW
modes.

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
AP_TECS: adapt for new airspeed variable names
APM_Control: pass in aircraft parameters and expose coordinate rate offset

this will make it possible to do rate based pitch control without
having a coordinated turn, for in ACRO mode

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
VARTest: adapt for new airspeed parameter names
Plane: pass aircraft parameters to attitude controllers

also cope with rename of airspeed min/max variables

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
APM_Control: added turn coordination flag and separate up/down integrators
Plane: use full pitch locking when roll is locked in ACRO

this attempts to avoid drift of the pitch with no stick input