Added arduino-nano to BOARD_INSUFFICIENT_MEMORY/BOARD_BLACKLIST following suit
of how arduino-uno is marked, as arduino-nano is mostly an Uno in a different
form factor.
The unification of a bigger stack for the atmega platforms
makes some boards to not have enough memory to provide
the big stack plus the application code.
It is possible though, to override the stack size to a
smaller amount if running the test is necessary.
Fixes#1708.
Currently involuntary preemption causes the current thread not only to
yield for a higher prioritized thread, but all other threads of its own
priority class, too.
This PR adds the function `thread_yield_higher()`, which will yield the
current thread in favor of higher prioritized functions, but not for
threads of its own priority class.
Boards now need to implement `thread_yield_higher()` instead of
`thread_yield()`, but `COREIF_NG` boards are not affected in any way.
`thread_yield()` retains its old meaning: yield for every thread that
has the same or a higher priority.
This PR does not touch the occurrences of `thread_yield()` in the periph
drivers, because the author of this PR did not look into the logic of
the various driver implementations.
