docs/design/part-TODO.txt: Update TODO.

docs/design/part-TODO.txt: Update TODO.

Original commit message from CVS:
* docs/design/part-TODO.txt:
Update TODO.

* gst/gstbin.c: (message_check), (bin_replace_message),
(bin_remove_messages), (is_eos), (gst_bin_add_func),
(update_degree), (gst_bin_sort_iterator_next), (bin_bus_handler),
(bin_query_duration_init), (bin_query_duration_fold),
(bin_query_duration_done), (bin_query_generic_fold),
(gst_bin_query):
Handle SEGMENT_START/DONE messages correctly.
More evolved query algorithm that handles duration queries
correctly.

* gst/gstelement.c: (gst_element_send_event), (gst_element_query),
(gst_element_get_state_func), (gst_element_abort_state),
(gst_element_commit_state), (gst_element_lost_state):
Some more debugging.

* gst/gstmessage.h:
Added doc.