Refactor the existing AP_IMU as AP_IMU_Oilpan (this will require changes in other projects TBD).
Add a shim IMU class for use by e.g. HIL protocol handlers.
This paves the way for a better handling of HIL_MODE_SENSORS as well as the mooted SPI-based oilpan IMU.
git-svn-id: https://arducopter.googlecode.com/svn/trunk@1342 f9c3cf11-9bcb-44bc-f272-b75c42450872