Original commit message from CVS:
* plugins/elements/gstmultiqueue.c:
(gst_multi_queue_loop):
Small fix.
(single_queue_overrun_cb), (single_queue_underrun_cb),
(single_queue_check_full), (gst_single_queue_new):
Implement single queue growth system.
This uses the extra-size properties, and will grow single queues by
that much if one goes full whereas there are others empty. This is
called extra-mode in the code.
When a single queue's levels go back below the initial max-size
limits, it is no longer in extra-mode. This is to ensure we don't
consume too much memory.
Fixes #399875