PX4 makefile: 'make configure_px4fmu' on px4 source before build

Pull Request #37
Ammended: squashed fixups down into a single commit

Signed-off-by: Pat Hickey <pat@moreproductive.org>
AC Fix BATT_CURR_PIN number
Rover: added SERIAL0_BAUD parameter
AP_InertialSensor: update PX4 driver to use read() method
HAL_PX4: fixed thread_running on failed startup
build: added configure_px4fmu to clean target
Copter: fixed test code warnings
Plane: run PX4 console at 57600
Plane: fixed test baro printout
AP_Baro: added accumulate method to PX4 driver, and fixed scaling
Arducopter: Backing out my changes for a new Loiter Repositioning mode.  Leonard and Jonathan's work will trump this.
Merge branch 'master' of git://github.com/diydrones/ardupilot