PR #488 introduced an error in a file license header in file sched/mqueue/mqueue.h. This commit fixe that error and in the course of doing that, changing the license header to the standard Apache 2.0 header. I am the author and copyright hold of all modified files.
* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
