Style.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
sh: Add new tests to the Makefile.
Invalidate the cache for the named posix semaphore when opened and
actual file storing the semaphore object is different from the file
created on the first open.  Store the file st_dev and st_ino members
of the struct stat in the semaphore structure on open, and compare
them with the attributes of the opened file to detect unlink and
re-creation.

This fixes an issue of sem_unlink(3) failing to flush the named entry
in the semaphore list for the current or remote process, making
sem_unlink(3) not correctly operating if the unlinked semaphore is
still opened.

Reported by:	Joris Giovannangeli <joris@giovannangeli.fr>
PR:	standards/189353
Reviewed by:	jilles (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
sh: In getopts, unset OPTARG where POSIX says we should.