[MEDIUM] Fix memory freeing at exit

New functions implemented:
 - deinit_pollers: called at the end of deinit())
 - prune_acl: called via list_for_each_entry_safe

Add missing pool_destroy2 calls:
 - p->hdr_idx_pool
 - pool2_tree64

Implement all task stopping:
 - health-check: needs new "struct task" in the struct server
 - queue processing: queue_mgt
 - appsess_refresh: appsession_refresh

before (idle system):
==6079== LEAK SUMMARY:
==6079==    definitely lost: 1,112 bytes in 75 blocks.
==6079==    indirectly lost: 53,356 bytes in 2,090 blocks.
==6079==      possibly lost: 52 bytes in 1 blocks.
==6079==    still reachable: 150,996 bytes in 504 blocks.
==6079==         suppressed: 0 bytes in 0 blocks.

after (idle system):
==6945== LEAK SUMMARY:
==6945==    definitely lost: 7,644 bytes in 137 blocks.
==6945==    indirectly lost: 9,913 bytes in 587 blocks.
==6945==      possibly lost: 0 bytes in 0 blocks.
==6945==    still reachable: 0 bytes in 0 blocks.
==6945==         suppressed: 0 bytes in 0 blocks.

before (running system for ~2m):
==9343== LEAK SUMMARY:
==9343==    definitely lost: 1,112 bytes in 75 blocks.
==9343==    indirectly lost: 54,199 bytes in 2,122 blocks.
==9343==      possibly lost: 52 bytes in 1 blocks.
==9343==    still reachable: 151,128 bytes in 509 blocks.
==9343==         suppressed: 0 bytes in 0 blocks.

after (running system for ~2m):
==11616== LEAK SUMMARY:
==11616==    definitely lost: 7,644 bytes in 137 blocks.
==11616==    indirectly lost: 9,981 bytes in 591 blocks.
==11616==      possibly lost: 0 bytes in 0 blocks.
==11616==    still reachable: 4 bytes in 1 blocks.
==11616==         suppressed: 0 bytes in 0 blocks.

Still not perfect but significant improvement.
diff --git a/src/appsession.c b/src/appsession.c
index 9b6868c..e1a01cc 100644
--- a/src/appsession.c
+++ b/src/appsession.c
@@ -27,7 +27,7 @@
 
 #include <proto/task.h>
 
-
+static struct task *appsess_refresh = NULL;
 struct pool_head *pool2_appsess;
 struct app_pool apools;
 int have_appsession;
@@ -87,17 +87,17 @@
 int appsession_task_init(void)
 {
 	static int initialized = 0;
-	struct task *t;
 	if (!initialized) {
-		if ((t = pool_alloc2(pool2_task)) == NULL)
+		if ((appsess_refresh = pool_alloc2(pool2_task)) == NULL)
 			return -1;
-		t->wq = NULL;
-		t->qlist.p = NULL;
-		t->state = TASK_IDLE;
-		t->context = NULL;
-		tv_ms_add(&t->expire, &now, TBLCHKINT);
-		t->process = appsession_refresh;
-		task_queue(t);
+
+		appsess_refresh->wq = NULL;
+		appsess_refresh->qlist.p = NULL;
+		appsess_refresh->state = TASK_IDLE;
+		appsess_refresh->context = NULL;
+		tv_ms_add(&appsess_refresh->expire, &now, TBLCHKINT);
+		appsess_refresh->process = appsession_refresh;
+		task_queue(appsess_refresh);
 		initialized ++;
 	}
 	return 0;
@@ -168,6 +168,13 @@
 		appsession_hash_destroy(&(p->htbl_proxy));
 		p = p->next;
 	}
+
+	if (appsess_refresh) {
+		task_delete(appsess_refresh);
+		task_free(appsess_refresh);
+		appsess_refresh = NULL;
+	}
+
 }/* end appsession_cleanup() */