CMake build causes gdb segfault.  Pulling out.

There is something subtley different between the bin file generated by the
ChibiOS provide Makefile and the current CMake build that results in the binary
having the same exact binary size but for some reason the CMake version causes
a segfault on Luke's machine for both 2012 and 2013 toolchains.  On Oliver's
machine, it only segfaulted with the 2013 toolchain.

Moving on to more important things and just going to use the standard Makefile.
Terminate write and control threads in shell thread.

Terminate both write and control threads in SampleAndControl::Stop()
instead of using nested chThdWait() commands.
Fix CMAKE_FIND_ROOT_PATH in CMake toolchain file.
Remove call to chThdSleepUntil() in control loop.

Occasionally, the control loop will take longer than expected (5ms) and
will chThdSleepUntil() missing the deadline and sleeping for a long
period of time instead.  The conditional statement in chThdSleepUntil()
will always evaluate to true since time and chTimeNow() are both
unsigned.
Discussed here: http://sourceforge.net/p/chibios/bugs/332/