cpu/nrf51822: fixed gpio driver
boards: added LED macro for pca1000 & yunjia-nrf
make: make doc clean target ignore failures
make: add clean, distclean for RIOT

distclean
removes all build products, also depends on docclean

clean
removes all build products for the current board

also, silence clean target from Makefile.include and let it ignore errors
make: remove $(CLEANFILES), it's superfluous
udp: fix byte order in sockaddr6_t

udp_recvfrom wrote the sender port number in host byte order into the
provided sockaddr6_t. Because all send functions expect the port number
in network byte order this introduces a superfluous conversion step in
case one wants to reuse the address for replying.

closes #1406
Merge pull request #1539 from LudwigOrtmann/distclean

make: [dist]clean
examples: add extern "C" to header `rpl_udp.h`
Fixes when a packet is not for me, but an interface is defined.
Merge pull request #1796 from RIOT-OS/ip_is_our_fix

Fixes when a packet is not for me, but an interface is defined.
net: Initial import of a packet wrapper for priority_queue
Merge pull request #1640 from authmillenon/packetqueue

net: Initial import of a packet wrapper for priority_queue
Merge pull request #1790 from BytesGalore/extern_C_in_headers_examples

examples: add extern "C" to headers
sys/net/pktqueue: fix doxygen
Merge pull request #1798 from LudwigOrtmann/pktqueue-doxygen

sys/net/pktqueue: fix doxygen
Merge pull request #1795 from sgso/byte-order-udp-sockaddr

udp: fix byte order in sockaddr6_t
Merge pull request #1720 from haukepetersen/fix_nrf_gpio

cpu/nrf51822: fixed gpio driver
Merge pull request #1722 from haukepetersen/fix_nrf_leds

boards: added LED macro for pca1000 & yunjia-nrf