added MPU-9150 support based on a hacked version of the i2cdevlib MPU6050 and AK8975 libraries

note that compilation is jerry-rigged, especially with the Arduino Wire
library; doing a `make clean && make` will result in 'cannot make
target', since arduino/makefile doesn't compile the Wire and Wire/util
code
Merge branch 'master' of github.com:ashima/embedded-atmel-twi