docs/design/part-states.txt: Some more docs.

docs/design/part-states.txt: Some more docs.

Original commit message from CVS:
* docs/design/part-states.txt:
Some more docs.

* gst/gstbin.c: (gst_bin_set_clock_func), (gst_bin_recalc_state),
(gst_bin_change_state_func), (bin_bus_handler):
Doc updates. Don't distribute the same clock over and over again.

* gst/gstclock.c:
* gst/gstclock.h:
Doc updates.

* gst/gstpad.c: (gst_flow_get_name), (gst_flow_to_quark),
(gst_pad_get_type), (gst_pad_push), (gst_pad_push_event),
(gst_pad_send_event):
* gst/gstpad.h:
Make probe emission threadsafe again.
Register quarks and move _get_name() from utils.
Doc updates.

* gst/gstpipeline.c: (gst_pipeline_class_init),
(gst_pipeline_change_state), (gst_pipeline_provide_clock_func):
Only redistribute the clock of it changed.

* gst/gstsystemclock.h:
Doc updates.

* gst/gstutils.c:
* gst/gstutils.h:
Moved the _flow_get_name() to GstPad.