porting: a few updates for the porting guide
docs: update the controller docs

Add the control bindings to the docs. Add a little more detail.
debugutils: fix order of caps on an unnegotiated link

headlabel is the sink_pad (where the link points to) and not the other way around.
structure: change argument name for docs
gstpipeline: fix failed assertion caused by seeking pipeline with NULL clock

Under certain GST_STATE_CHANGED_PAUSED_TO_PLAYING transitions, a pipeline with
a NULL clock will fail an assertion due to an unchecked call to gst_object_ref().
This is fixed by simply adding a check and only ref-ing if the clock is not NULL.

https://bugzilla.gnome.org/show_bug.cgi?id=693065
basesink: handle sync of EOS after item without duration

After a buffer or GAP without duration, an EOS event should be rendered
immediately instead of waiting for the end of the segment.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=692868
tests: add basesink test
bin: reset GValue from iterator after usage
bin: remove old comment

The iterators now return a GValue and not the object directly anymore.
element: remove old docs about iterators
controlbinding: error handling for binding controlsources to wrong properties

Add warning if property is not suitable for controlling. When adding a control-
binding check that pspec!=NULL.
docs: add more porting details
baseparse: improve PTS interpolating

... and tracking of DTS.  Fixes cases where PTS is locked on to the
DTS of an incoming buffer with no PTS with invalid data, leading to
no outgoing PTS (since it is not allowed smaller than DTS).

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=691481
gstvalue: Adding offset to GstSegment serialize/deserialize.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=693587
compat: kill more uses of gst_pad_set_caps()
bin: Let gst_bin_send_event() send events to ghost pads as well
bin: query sink elements and source pads of the bin

gst_bin_query() now forwards the query to the source pads as well if
none of the sinks of the bin satisfied the query. This helps in the
case of DURATION queries done a bin containing a source element.

Fixes bug 638749
adapter: Add gst_adapter_prev_[pd]ts_at_offset()

Original patch written by Michael Smith <msmith@rdio.com>.

API: gst_adapter_prev_pts_at_offset()
API: gst_adapter_prev_dts_at_offset()
baseparse: add gst_base_parse_set_ts_at_offset()

Sets the buffer timestamps based on last seen timestamps at a
particular offset into the frame.

API: gst_base_parse_set_ts_at_offset()
baseparse: Fix doc typo