Renamed unlock_the_lock to scoped_unlock

Signed-off-by: K-ballo <k@fusionfenix.com>
Renamed hpx/util/unlock_lock.hpp to scoped_unlock.hpp

Signed-off-by: K-ballo <k@fusionfenix.com>
Merge pull request #813 from K-ballo/scoped_unlock

Scoped unlock