sem_open: Make sure to fail an O_CREAT|O_EXCL open, even if that semaphore is already open in this process.
sem_open: Make sure to fail an O_CREAT|O_EXCL open, even if that semaphore
is already open in this process.

If the named semaphore is already open, sem_open() only increments a
reference count and did not take the flags into account (which otherwise
happens by passing them to open()). Add an extra check for O_CREAT|O_EXCL.

PR:		kern/166706
Reviewed by:	davidxu
MFC after:	10 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase