Fix a race between scheduling a new request onto an idle connection and

Fix a race between scheduling a new request onto an idle connection and
closing the same connection.

When closing an idle connection that connection needs to be moved off the
idle queue and back onto the active queue. Do this in the two possible
cases (directly in http_close() and in http_handle() for the STATE_IDLE
case). In both cases it is possible that the system needs to repoll the
connection and while waiting a request could be scheduled on that connection
if it remains on the idle queue.

Problem hit by job@
OK tb@