Fixes

* src/sasatom_powerpc.h (__arch_compare_and_swap): Use isync.
* src/tests/sphsinglepcqueue_tt.c (test_unit): Use SPH_TIMERTEST_VERIFY.
* src/tests/sphsinglepcqueue_ttt.c: Add tests for 2, 3, 4 thread cascade.
Add examples of hysteresis based on queue depth.