vtimer: fix callback usage

There is no need to test the "handler" set in the vtimer struct, and
have some code executed then. We just can make the code to execute the
handler. To lengthy `if else if`, just a call.
ccnl: fixed commenting style
ccnl: eliminated empty translation unit warning
Reset the SAM3X8E before flashing
so as to avoid some hangups in the flashing process
core/msg: revert part of #1285

use m->sender_pid instead of sched_active_pid again
undoes the optimization intended by #1285
fixes uint/int warning
core/msg: set m->sender_pid before it is used

fixes `msg_send_to_self` condition
SQUASHME: do it right
core/thread: remove thread_create_arg from header

It's just a leftover from #856
Merge pull request #1397 from LudwigOrtmann/thread_fixup

core/thread: remove thread_create_arg from header
core: removed duplicated hwtimer_arch.h
Merge pull request #1398 from haukepetersen/fix_hwtimer_arch

core: removed duplicated hwtimer_arch.h
sys/transceiver: fix t9r_register API compliance
sys/transceiver: implement transceiver_unregister
sys/transceiver: refactor un/register

remove race conditions
make less restrictive (allow double-un/registers)
make loops more readable
sys/transceiver: use size_t instead of u8 in loops
Merge pull request #1395 from LudwigOrtmann/transceiver_unregister

sys/transceiver: add transceiver_unregister and refactor transceiver_register
make: move exported make vars to one place
make: don't use export on example makefiles
Merge pull request #1109 from Kijewski/make-exports

make: no "unfriedly" `exports` in the application's Makefile
Merge pull request #1387 from LudwigOrtmann/msg_fixup

core/msg: clean up after #1285