posix: move posix semaphore in posix module
rename test for posix semaphore
correct copyright and doxygen
Merge pull request #845 from mehlis/sem-to-posix

posix: move posix semaphore in posix module
test_hwtimer: print out message explaining test

fixes: #791
Merge pull request #815 from LudwigOrtmann/issue_791

test_hwtimer: print out message explaining test