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.
AP_Baro: ask for maximum poll rate for PX4
HAL_PX4: added APM startup script
build: added EXTERNAL_SCRIPTS to PX4 build
HAL_PX4: switched scheduler to use a pthread

this allows the timer tasks to access file descriptors in the main APM
task, which makes writing PX4 device drivers much easier
HAL_PX4: added AnalogIn driver

this allows airspeed to work on a PX4
HAL_PX4: start adc driver in rc.APM
Plane: setup PX4 airspeed analog port
HAL_PX4: enabled AnalogIn driver
Plane: cleanup driver declaration

remove a lot of the #if nesting