make: don't ignore failures in for loops

apply 9b61d95545446675ae136cf64f5c3af2d1cc6e22 to oonf_api
remove trailing whitespaces
silence git warning about detached head

use reset --hard to check out the desired revision
remove unnecessary comments from Makefile

remove leftovers from the example Makefile, they are unnededly printed during the build
fix oonf_api build with GNU Make 4.0

fixes #884
abort on error when patching oonf_api
Merge pull request #895 from benpicco/oonf_fix

make: don't ignore failures in for loops, fix build with make 4.0 and minor cleanups