PX4: systemreset() now takes a boolean argument

this chooses whether to stay in the bootloader
PX4: hide the mkdir error on boot
PX4: fixed test logic for console
PX4: changed to new names for board modules
PX4: implement APM/nostart in rcS

this keeps the same shell on nostart, avoiding relying on nshterm
PX4: added a sleep before probing for PX4IO update

this makes boot more reliable for some unknown reason
PX4: use a minimum transmit buffer for UARTs of 512 bytes

this avoids writes stalling on the GPS port. We can't afford this
memory on APM2, but we can on PX4, and it means that while the GPS is
blocking at startup it doesn't cause any scheduler slips
PX4: avoid writing px4io update log to SD card

this seems to be one of the causes of lockups of the FMU
AP_InertialSensor: switch to non-averaging system for PX4 IMUs

always use the latest value, based on a lowpass filter in the driver
PX4: make upload targets depend on build targets

this allows for "make px4-v1-upload" for faster development cycles
AP_InertialSensor: switch PX4 driver to fixed time per sample model

this makes the driver much simpler, and does away with the need for an
accumulate function
PX4: changes to startup after stacksize fix

we can redirect to FAT fs again, and remove the sleep lines
PX4: remove the use of symlinks in PX4 build

this should make it more windows friendly
Build: move BUILDROOT inside SKETCHBOOK

this allows for relative paths in the px4 build
PX4: speed up the build a lot

this avoids removal of built objects and dependencies by allowing the
PX4 build system to put all objects and dependencies in the per-board
build directories
PX4: ensure storage buffer is DMA aligned

this helps for boards which use DMA for FAT IO
PX4: disable sensors module

this isn't needed for APM, and fails to build
AP_Airspeed: list MEAS airspeed in ARSPD_PIN docs
AP_Baro: use fabs() not abs()

thanks to Randy for spotting this
PX4: try to start meas_airspeed driver