Lock the cells for init,kick and time-step tasks.

src/task.c

@@ -283,6 +283,10 @@ void task_unlock(struct task *t) {
   /* Act based on task type. */
   switch (type) {
 
+    case task_type_init:
+    case task_type_kick1:
+    case task_type_kick2:
+    case task_type_timestep:
     case task_type_drift:
       cell_unlocktree(ci);
       cell_gunlocktree(ci);
@@ -355,6 +359,10 @@ int task_lock(struct task *t) {
 #endif
       break;
 
+    case task_type_init:
+    case task_type_kick1:
+    case task_type_kick2:
+    case task_type_timestep:
     case task_type_drift:
       if (ci->hold || ci->ghold) return 0;
       if (cell_locktree(ci) != 0) return 0;