rewrote mpu6050 revision sensing code to match that of eMPL from Invensense.
Also changed scalefactor for acc to 256/512 to match multiwii code. untested/etc, proceed with caution.

git-svn-id: https://afrodevices.googlecode.com/svn/trunk/baseflight@276 7c89a4a9-59b9-e629-4cfe-3a2d53b20e61