this will allow us to log the Product ID in tlogs

this exposes the product ID to the IMU Layer

Rev C have non standard scaling factor that is 1/2 of the data sheet
Rev D chips conform to the specification

this will be used to avoid races in driver initialisation

This reduces the compass's default authority over the yaw direction by half

this moves the enums to make them less order sensitive

this should autodetect 1.0 versus older builds

this was preventing building MAVLink 1.0 with the arduino GUI as we
can't set cpp defines

these are a very useful reference for the current headers in the code

this fixes the camera control code which was broken by a previous
import

this allows logging of the actual servo output values. The radio_out
method previously used doesn't take account of the various override
mechanisms available via waypoints

this buffers up _omega_I changes in _omega_I_sum over a period of 10
seconds, applying the slope limit only when _omega_I_sum is
transferred to _omega_I.

The result is a huge improvement in the ability of _omega_I to track
gyro drift over the long term.

the 'drop z' method reduced the impact of noise on omegaI, but it also
made us more sensitive to errors in accelerometer calibration and
scaling, as demonstated by the logs from Gabor here:

  http://diydrones.com/xn/detail/705844:Comment:834373

Simulation testing shows that the other noise suppression methods
applied in the DCM code, in particular the slope limiting on omegaI
the removal of the weighting and the upcoming use of a _omega_I_sum
buffer have reduced the impact of noise enough that we can now safely
include z in the acceleration calculation.

DataFlash_APM2 - moved CS_inactive call (which disables the dataflash) from the beginning to the end of all methods.  This means the dataflash does not monopolize the SPI bus.
    Also formatting changes to use tab instead of space. Sorry, should have done this as a separate check-in to the above changes.

this allows users to change the yaw gain in DCM

this adds local and remote radio noise levels