docs/design/part-seeking.txt: Some small additions.

docs/design/part-seeking.txt: Some small additions.

Original commit message from CVS:
* docs/design/part-seeking.txt:
Some small additions.

* gst/base/gstbasesink.c: (gst_base_sink_handle_object),
(gst_base_sink_get_times), (gst_base_sink_do_sync),
(gst_base_sink_activate_push), (gst_base_sink_activate_pull):
* gst/base/gstbasesink.h:
discont values are gint64, handle the math correctly.

* gst/base/gstbasesrc.c: (gst_base_src_loop):
Make the basesrc report error if the source pad is not linked.

* gst/gstqueue.c: (gst_queue_link_src), (gst_queue_chain),
(gst_queue_loop), (gst_queue_handle_src_query),
(gst_queue_src_activate_push):
Make queue collect data even if the srcpad is not linked.
Start pushing out data as soon as it is linked.

* gst/gstutils.c: (gst_element_unlink), (gst_flow_get_name):
* gst/gstutils.h:
Added gst_flow_get_name() to ease error reporting.