cpu/nrf51822: fixed gpio driver
boards: added LED macro for pca1000 & yunjia-nrf
make: del no-delete-null-pointer-checks for clang++

This PR enables the use of clang++ to compile C++ projects by adding
`CXXUWFLAGS += -fno-delete-null-pointer-checks`, if `${CC}` understands
`-fno-delete-null-pointer-checks` but `${CXX}` does not.
core: Provide functions for different byte orders

Rationale: see #1586.
tests: Add unittests for byteorder.h
tests: fix bad copy+paste in tests-core.h
atmega_common: add ENOTSUP and ECANCELED to errno.h
drivers: Provide basic interface for all network devices
tests: Add functionality test for netdev_base
Merge pull request #1492 from authmillenon/net-dev-base

drivers: Introduce a general interface for network device drivers
tests: fix netdev test
Merge pull request #1761 from authmillenon/netdev-fix

tests: fix netdev test
cpu/stm32f0: removed leftovers from slave mode
Merge pull request #1713 from haukepetersen/fix_stm32f0_spi

cpu/stm32f0: removed leftovers from slave mode
Notify about dropped packets

Added debug output that warns about packets that are dropped
because the transceiver buffer was full or because the transceiver
failed to notify aiting upper layers.
Merge pull request #1755 from Lotterleben/transceiver_debug_clean

transceiver: notify about dropped packets
board/iot-lab_M3: fixed default terminal device
Merge pull request #1760 from haukepetersen/fix_iotlab_term

board/iot-lab_M3: fixed default terminal device
redbee-econotag: don't print noisy warning
make: Centralize color use