Per-thread scheduling. Closes #682.

Tasks are spawned on a random thread. Currently they stay there, but
we should add task migration and load balancing in the future. This
should drammatically improve our task performance benchmarks.

src/rt/rust_util.h

@@ -126,8 +126,9 @@ next_power_of_two(size_t s)
 
 // Initialization helper for ISAAC RNG
 
+template <typename sched_or_kernel>
 static inline void
-isaac_init(rust_scheduler *sched, randctx *rctx)
+isaac_init(sched_or_kernel *sched, randctx *rctx)
 {
         memset(rctx, 0, sizeof(randctx));