transceiver: fix check for existence

The transceiver check if it is already running when initializing.
However, this check was done by comparing its pid for >= 0, which is not
sensible anymore since valid PIDs only start at 1.
native: fix and improve term-valgrind flags
Merge pull request #1602 from OlegHahm/transceiver_init_pid_check

transceiver: fix check for existence
native: add stack smashing protection

When `DEVELHELP` is defined, add `-fstack-protector-all`.
board/pca1000[0|5]: enabled RNG peripheral
cpu/nrf51822: added RNG driver
Merge pull request #1603 from LudwigOrtmann/native-valgrindoptions

native: fix and improve term-valgrind flags
fix license headers in non-.c files
tests: let license checker check cpp files, too
Merge pull request #1570 from LudwigOrtmann/native-ssp

native: add stack smashing protection
cpu/stm32f4: added random number generator driver
board/stm32f4discovery: enabled RNG driver
Merge pull request #1611 from haukepetersen/add_stm32f4_random

cpu/stm32f4: added random number generator driver
Merge pull request #1607 from haukepetersen/add_nrf_random

cpu/nrf51822: added random number generator driver
Merge pull request #1608 from LudwigOrtmann/fixmorelicenseheaders

Fix more license headers
tests: fix lifo unittest

The API was violated resulting in an array overrun.
Merge pull request #1614 from LudwigOrtmann/unittests_fix

tests: fix lifo unittest
sys/cbor: set isdst to undefined after strptime

CBOR does not specify the daylight saving time adjustment.
tests: fix cbor unittest

Some member of `struct tm val` were not set, resulting in undefined
behavior.