native: fix and improve term-valgrind flags
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
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
dist/tools: add cppcheck script

enables easy linting of the whole tree or just one branches changes against
another
tests: enable cppcheck for PR in travis