native: forced debug message for SIGUSR1
rpl: addr_str not renamed to addr_str_mode
In PR #1404 addr_str was renamed to addr_str_mode,
but at some places it was still referenced as addr_str.
When enabling debug messages, the compiler complains.
native: cleanup irq_cpu, native_cpu debug output
doc: periph/dac: fix typo
Merge pull request #2135 from LudwigOrtmann/doxygen-dac

doc: periph/dac: fix typo
Merge pull request #2134 from cgundogan/rpl_addr_str_debug_fix

rpl: addr_str not renamed to addr_str_mode
Merge pull request #2133 from LudwigOrtmann/native-doc-update

Native doc update