Fixup for #685

- use DEVELHELP for native as well
- fix function name in documentation
- improve documentation language/spelling
Include kernel.h for inet_pton for MSP-430
Merge pull request #790 from LudwigOrtmann/fixup_685

core: fixup for 685
Merge pull request #808 from authmillenon/inet_pton_msp_430_fix

Include kernel.h for inet_pton for MSP-430