New remote control commands: dump_active, stats

dump_active shows the currently executing tasks.
e.g.:

    {"tasks.add": 2, "tasks.create_user": 3}

means there are 2 add tasks, and 5 create_users tasks currently executing.

stats shows some statistics and general information about the worker.

celery/worker/control/builtins.py

@@ -4,6 +4,7 @@ from celery import conf
 from celery.backends import default_backend
 from celery.registry import tasks
 from celery.utils import timeutils
+from celery.worker import state
 from celery.worker.revoke import revoked
 from celery.worker.control.registry import Panel
 
@@ -116,6 +117,19 @@ def dump_reserved(panel, **kwargs):
     return info
 
 
+@Panel.register
+def dump_active(panel, **kwargs):
+    from celery.worker.state import active
+    return active
+
+
+@Panel.register
+def stats(panel, **kwargs):
+    return {"active": state.active,
+            "total": state.total,
+            "pool": panel.listener.pool.info}
+
+
 @Panel.register
 def dump_tasks(panel, **kwargs):