Merge branches 'doc.2015.10.06a', 'percpu-rwsem.2015.10.06a' and 'torture.2015.10.06a' into HEAD

doc.2015.10.06a:  Documentation updates.
percpu-rwsem.2015.10.06a:  Optimization of per-CPU reader-writer semaphores.
torture.2015.10.06a:  Torture-test updates.