[MAJOR] replace ultree with ebtree in wait-queues

The ultree code has been removed in favor of a simpler and
cleaner ebtree implementation. The eternity queue does not
need to exist anymore, and the pool_tree64 has been removed.

The ebtree node is stored in the task itself. The qlist list
header is still used by the run-queue, but will be able to
disappear once the run-queue uses ebtree too.
diff --git a/src/checks.c b/src/checks.c
index eff0df0..91db026 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -850,9 +850,7 @@
 
 			s->check = t;
 
-			t->wq = NULL;
-			t->qlist.p = NULL;
-			t->state = TASK_IDLE;
+			task_init(t);
 			t->process = process_chk;
 			t->context = s;