docs/design/part-negotiation.txt: Small doc update.

docs/design/part-negotiation.txt: Small doc update.

Original commit message from CVS:
* docs/design/part-negotiation.txt:
Small doc update.
* docs/libs/gstreamer-libs-sections.txt:
* libs/gst/base/gstbasesink.c: (gst_base_sink_class_init),
(gst_base_sink_pad_getcaps), (gst_base_sink_pad_setcaps),
(gst_base_sink_init), (gst_base_sink_set_blocksize),
(gst_base_sink_get_blocksize), (gst_base_sink_set_property),
(gst_base_sink_get_property), (gst_base_sink_needs_preroll),
(gst_base_sink_loop), (gst_base_sink_pad_activate),
(gst_base_sink_negotiate_pull), (gst_base_sink_pad_activate_pull),
(gst_base_sink_change_state):
* libs/gst/base/gstbasesink.h:
Add blocksize property and methods to control the amount of data
to pull.
Negotiate first before activating upstream in pull mode so that they can
negotiate themselves.
When we operate in pull mode, we only accept the caps that we
negotiated.
Make the sink go ASYNC to PAUSED, like all other sinks.
API: GstBaseSink::gst_base_sink_set_blocksize()
API: GstBaseSink::gst_base_sink_get_blocksize()
API: GstBaseSink::blocksize
* libs/gst/base/gstbasesrc.c: (gst_base_src_wait_playing),
(gst_base_src_set_live), (gst_base_src_is_live),
(gst_base_src_set_format), (gst_base_src_query_latency),
(gst_base_src_set_blocksize), (gst_base_src_get_blocksize),
(gst_base_src_set_do_timestamp), (gst_base_src_get_do_timestamp),
(gst_base_src_set_property), (gst_base_src_get_property):
* libs/gst/base/gstbasesrc.h:
Add typechecking in public API functions.
Add methods to control the blocksize in subclasses.
API: GstBaseSrc::gst_base_src_set_blocksize()
API: GstBaseSrc::gst_base_src_get_blocksize()