moved debugging statements from header to c file

Additionally, declaring the stacks as static.
amendment - to be squashed
tests: add test that shows sequence of received messages
test_thread_msg_seq: add missing main() return statement
core:mutex: allow idle thread to use mutexes
native: config_load: set PID as id, net address
core: kernel_init: call config_load in kernel_init
Merge pull request #817 from kaspar030/tests_msg_sequence

tests: add test that shows sequence of received messages
Merge pull request #792 from OlegHahm/etx_fixes

rpl: moved debugging statements from header to c file
Fix issue #896
Merge pull request #700 from LudwigOrtmann/sniper_700

kernel_init: config_load, native: config_load: set id/address to PID
Merge pull request #902 from Kijewski/issue-896

Fix issue #896
Merge pull request #859 from Kijewski/mutex-trylock-error

core:mutex: allow idle thread to use mutexes