Magnetometer data is not update

Magnetometer is not updated during a read operation, because the function "lsm303d_mag::measure" is not called.

”!!!JUST A GUESS!!!“
Merge pull request #1023 from ultrasystem/patch-1

Magnetometer data is not update
Hotfix: Fix scaling for battery current
Merge branch 'master' of github.com:PX4/Firmware
Hotfix: Better microSD reporting