whitespace and spelling fixes, no functional changes
Schedule fibers in the order they are asynced or unblocked.  Earlier behavior was always to start newly-asycned tasks before resuming existing tasks, so existing tasks could be starved if there was a steady stream of new tasks created.  Now all tasks are started or resumed in the order they are created or unblocked.
Add missing include
Convert ready_head (list of fibers able to run immediately) into a priority heap
Remove #ifdefed-out code