cpu/samd21: add i2c periph implementation
sixlowpan: remove redundant assignment
sixlowpan: handle malloc error

The return value of malloc wasn't checked before, resulting in
possibly undefined behavior.
Merge pull request #2187 from LudwigOrtmann/sixlowpan-malloc

sixlowpan: handle malloc error
native: workaround for missing __builtin_bswap16

Implements a workaround for
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624

This is present in current versions of ubuntu 12.04 and debian 7.7 (stable).
Merge pull request #2170 from LudwigOrtmann/native-bswap

native: workaround for missing __builtin_bswap16
make: migrate OS variable for COLOR_ECHO too
Merge pull request #2196 from thomaseichinger/fix_color_echo

make: migrate OS variable for COLOR_ECHO too
Merge pull request #2016 from bapclenet/master

cpu/samd21: I2C driver implementation (Master mode)