plugins/elements/gstqueue.*: Be smarter when calculating the current amount of data...

plugins/elements/gstqueue.*: Be smarter when calculating the current amount of data in the queue by measuring the dif...

Original commit message from CVS:
* plugins/elements/gstqueue.c: (gst_queue_class_init),
(update_time_level), (gst_queue_locked_flush),
(gst_queue_handle_sink_event), (gst_queue_chain),
(gst_queue_push_one), (gst_queue_loop):
* plugins/elements/gstqueue.h:
Be smarter when calculating the current amount of data in the queue by
measuring the difference between start and end timestamps (in running
time) inside the queue. Fixes #432876.
API: GstQueue::pushing to notify elements that we are pushing data again
since the running signal is rather broken for this purpose.