Made intrusive_priority_queue_node_t not use virtual functions, and some other aesthetic changes.
Merge branch 'next' into sam_priorityqueue
Made us require that left_is_higher_priority take const parameters.
Merge branch 'next' into sam_priorityqueue
Merge branch 'next' into sam_priorityqueue
Fixed is_higher_priority_than function after intrusive_priority_queue_node_t stopped using virtual methods.