[conf] fixedwing ahrs use gps course instead of mag for heading by default
[ahrs] warn if PERIODIC_FREQUENCY is lower than AHRS freqs
[config] better warning message and update example airframe
[plotter] open new plotter with parent settings
[plot] draw curves at low resolution when moving/selecting in log plotter

much faster when dealing with huge logs
[boards] add driver for KroozSD BigRotorcraftEdition

- IMU with memsic MXR9500 accelerometer
- set mag correct freq to 75Hz for krooz_sd_x

closes #586
[build] ARM toolchain/Makefile cleanup

- possible to explicitly pass a PREFIX to use other toolchain
  default for PREFIX is arm-none-eabi or arm-linux-gnueabi
- print meaninfull error if arm-linux toolchain is not found
- printcommands prints only CC and GCC version
- remove obsolete find OpenOCD stuff
[rotorcraft] fix some attitude ref telemety message sending
[PPRZ CENTER] Added some more verbose io watch callbacks.

Trying to investigate the issue of immediately closing processes in
paparazzi center on mac os x Mountain Lion and Mavericks.
[PPRZ CENTER] Different approach for io_watch signal handling.

This time we have only one watch reacting to OUT and HUP, wheras it is
ignoring OUT signal and running callback only for HUP.
[PPRZ CENTER] Capture more of the IO signals.

Trying to gather a bit more data on the signal behavior.
[PPRZ CENTER] Fixed detection of child processes exitting on Mac OS.

We are now checking if the input channel is empty when receiving the IN
callback. If that is the case we assume that the child process exitted,
ond call the close process callback that normally is treggered by the
HUP callback.

Some background: On OS X glib is using it's own implementation of poll
that does not generate the HUP signal. (It would be possible to add this
functionality modelled after the SSH implementation of bsd_poll) The
glib implementation does generate IN signal when the pipe get's closed.
So we can just check if the input channel is empty and if that is the
case infer that the pipe got closed.