changed parameters form `kernel_pid_t` to `int`
dist/tools: add cppcheck script

enables easy linting of the whole tree or just one branches changes against
another
board/pca1000x: added/fixed dist scripts

- pca10000: added author to debug.sh
- pca10005: added debug and reset scripts
- pca10005: fixed flash script
- pca10005: adjusted env vars in Makefile.include
Fix thread_yield by avoiding the (too) early re-enablement of IRQ,
that is: before the newly selected thread's context is totally restored
Prevent the compiler to add an unwanted prologue in thread_yield()
Fix the race condition when an interruption occured at the beginning
of thread_yield(), i.e.: just after SR(R2) was pushed but before
the rest of the suspended thread's context was pushed!
SQUASHME: file(line) -> file:line

Addresses https://github.com/RIOT-OS/RIOT/pull/1604#discussion_r16936195
iot-lab_M3: extend debug target for iot-lab_M3
SQUASHME: kill openocd by PID
Merge pull request #1629 from thomaseichinger/iot-lab_debugger++

iot-lab_M3: extend debug target for iot-lab_M3
core: priority_queue: simplify inheritance
SQUASHME: add documentation
cpu: atmega: doxygen: blacklist upstream headers
Merge pull request #1642 from N8Fear/avr-libc-fix-doxygen

cpu: atmega: doxygen: blacklist upstream headers
SQUASHME: undo accidental commit of timex.h
SQUASHME: tool -> tools path typo
Merge pull request #1604 from LudwigOrtmann/cppcheck-script

dist/tools: add cppcheck script
vtimer: no needless type casting

Compare https://github.com/RIOT-OS/RIOT/pull/1639#issuecomment-54713048
and following discussion.
unittests: make: Fix unittests for branch changes

Changing between branches in git typically leaves directories empty and
does not remove them. If you have different unittests in different
branches this leads to an error in building them, since the current
configuration expects a Makefile in all `tests-*` directory. This change
configures Make to search for a Makefile in `tests-*` rather than just
assuming that there is one.
Fixed comments