MINOR: task: Rename run_queue and run_queue_cur counters

<run_queue> is used to track the number of task in the run queue and
<run_queue_cur> is a copy used for the reporting purpose. These counters has
been renamed, respectively, <tasks_run_queue> and <tasks_run_queue_cur>. So the
naming is consistent between tasks and applets.

[wt: needed for next fixes, backport to 1.7 and 1.6]
diff --git a/src/stream.c b/src/stream.c
index 08f3aa9..055cc23 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -449,7 +449,7 @@
 	struct stream *sess, *bak;
 
 	list_for_each_entry_safe(sess, bak, &buffer_wq, buffer_wait) {
-		if (rqlimit <= run_queue)
+		if (rqlimit <= tasks_run_queue)
 			break;
 
 		if (sess->task->state & TASK_RUNNING)