this adds local and remote radio noise levels

AP_MotorsMatrix - fixed stability patch issue in which it would not limit a motor's output unless an opposite motor had been defined.  This would only have affected Y6 frames.

3dr Radio support
update mavlink library

3DR R
setup layout - thanks andrew.

update message definitions
fix radio screen

AP_Motors - fixed last "shadowing" compiler warning caused by badly named parameter in auto_armed method.

AP_MotorsMatrix - fixed another compiler error regarding shadowing a variable.  Fixed by removing those  the angle and direction arrays which weren't even used

AP_MotorsHeli - fixed compiler warning re move_swash function declared with int parameters in .h file but actually using int16_t in .cpp file.  They're the same in arduino but perhaps the build checker is a little more strict that Arduino.

AP_Motors - fix compiler warning re shadowing a variable caused by badly named parameter in armed function.
Another compiler warning fixed in AP_MotorsMatrix.cpp caused by declaring "i" twice.

ArduCopter - removed unused motor pde files including heli.pde, motors_hexa.pde, motors_octa.pde, motors_octa_quad.pde, motors_tri.pde and motors_y6.pde

ArduCopter - test.pde - changed references "motor_armed" to "motors.armed()" as part of move to AP_Motors library.
Change to ESC initialisation calls to use motors.throttle_pass_through method of AP_Motors class.

ArduCopter - system.pde - changed references to "motor_armed" to "motors.armed()" as part of the move to use AP_Motors library.

ArduCopter - setup.pde - changed cli for helicopter to call the new AP_Motors class's parameters instead of the global parameters.
changed init_esc to call the AP_Motor's class's "throttle_pass_through" function.

ArduCopter - radio.pde - changed motor initialisation to set update rate, frame orientation, min and max throttle to AP_Motors class.
Note: perhaps the motors speed at least should be moved to a parameter within the motors class.
output_min function greatly simplified as this is handled by the AP_Motors class.

ArduCopter - motors.pde - changed references to "motor_armed" to "motors.armed()" because we've moved to using the AP_Motors class.
Simplified set_servos_4 function which was responsible for calling "output_motors_armed" or "output_motors_disarmed" as this determination as to whether the motors are armed or not is handled within the AP_Motors class.

ArduCopter - removed references to MOT_1 etc as these are now within the AP_Motors class (i.e. MOT_1 has become AP_MOTORS_MOT_1)

ArduCopter - increased firmware version to 118.  Removed nearly all heli parameters as these are all created by the AP_MotorHeli class now.
Note: we cannot move the heli_servos to the AP_MotorHeli class yet because of a small issue in the parameters class.

ArduCopter - Log.pde - changed MOT output to dataflash to take values from AP_Motors class's motor_out array instead of the global motor_out array.

ArduCopter - GCS_Mavlink.pde - changed output to ground station to use new AP_Motor's class motors array inplace of the global "motor_out" array.

ArduCopter - Attitude.pde - moved heli_get_angle_boost from heli.pde (which will be removed) to Attitude.pde.  In fact we should combine heli_get_angle_boost and the regular get_angle_boost.

Remove global motor_filtered and motor_out arrays.
Removed all global heli variables.
replace "motor_armed" with "motors.armed()"
removed output to rc_4 for tri because this is now handled by AP_MotorsTri class

add stab kd ch6
fix mono/linux serial port list

     1. it's step towards rearchitecting the current code base ahead of a move to RTOS.
     2. internally it uses a MatrixTable for the Quad, Octa, OctaQuad, Y6 frames.
     3. it implements the missing stability patch for Octa and OctaQuads (still missing for Y6)

Later check-ins will incorporate into the main ArduCopter code.

This allows for arbitrary stream rates, and supports flow control if
you are using a 3DR radio

this makes it possible to fetch parameters with very low air data
rates

streams can now be requested at any multiple of 20ms. So if you ask
for a stream at 7Hz then you will get it at close to 7Hz.

ArduCopter - CH6 tuning - changed Roll/Pitch Rate D tuning to use the user supplied tuning range instead of the range / 100.
             also changed heli_ext_gyro_gain to make it use the tuning range directly.

the GPS_STATUS message is a massive waste of bandwidth, but it is the
only message that tells us the number of visible satellites. So only
send it if that information changes.

This makes MAVLink work better at low baud rates

this allows us to put a serial port into non-blocking mode, so that
writes that don't fit in the transmit buffer are dropped. This will be
used in flight to prevent stray printf() calls from causing large time
delays in the code

the 128 byte serial transmit buffer was causing significant problems
with queueing of mavlink messages. With 256 bytes we can fit a lot
more messages out in each pass of the code, which makes telemetry more
efficient

As we discussed on the dev call, we now have enough free ram for this
to be worthwhile