Changed from using mutex_is_locked() to a new mutex_owned(), in support of the

Changed from using mutex_is_locked() to a new mutex_owned(), in support of the
Solaris MUTEX_HELD() macro.  The former was merely testing whether the mutex was
locked, whereas the real test needed here is whether the mutex is held by the
current thread.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>