the device ioctl returns -ENOTTY when it hasn't handled the command

Add FIONWRITE to allow applications to sniff the amount of writable space on a descriptor. Implement this for serial devices only.

this is used by the APM build

Updated PX4IOAR start script

Untangle the DSM decoder from the input source priority logic, clean up input handling some more.

Made MPU-6000 gyro optional

Don't call ::close on ORB publication handles.

Fix several aspects of the PWM output driver; enable auto-reload, use named constants for various control bits, and use a more polite mechanism at disarm time to avoid runt pulses.

This may address an issue we've seen where we get occasional malformed PWM output pulses, possibly due to a race between compare updates and the timer.

Whitespace.

Greatly sped up Matlab import script

Greatly sped up Matlab import script, a 17min flight now takes 2secs to import instead of more than the actual flight time

Added more LED state logic and improve code.

The LED will now also indicate when the FMU is ARMED. Switched to using
a 16-bit value where each bit indicates what state the LED should be
in.

Add new safety switch LED blink sequence when both FMU and IO are armed

If both the FMU and the IO board are armed then the secure switch will
blink two times quickly then a pause followed by two quick blinks and
so on.

Adjust the control mapping from DSM receivers to correspond to the standard PPM control mapping for channels 0-4.

Fix breakage to the DSM parser introduced with the input prioritisation logic.  Back out to a "any input wins" strategy; connecting multiple receivers to I/O at the same time is currently not supported (read: strange things will happen).

BlinkM driver

Added delay test to measure comm delays with a led / scope

Made sure IO and FMU obey the lockdown flag when arming motors

#61 px4io spektrum decoder

Cleaned up different uorb topics, cleaned up excessive stack sizes

Fixed missing heading for mtkcustom and nmea