This reverts commit 93b83333.

Reverting since this fails on a fresh checkout. Also, we shouldn't
depend on possibly translated strings.

Also mention decodebin2, uridecodebin, and playbin2

When we start a flushing step operation, forget about the previous stream time
so that the position reporting works correctly.

When it is shutting down a pipeline after ctrl-c, set pipeline to
paused before waiting for the main loop to complete all pending
transactions.  Fixes #584657.

If some part of the pipeline is generating signals or idle functions
at a fast rate, waiting for a main loop iteration may never return.

Use string_warp/unwrap to escape delimiters, otherwise deserialisation fails.
Also move GST_ASCII_IS_STRING to private header to avoid keeping it in sync.
Also use '\0' when terminating a string for better readability.

Store the timestamp of the buffer after prerolling. While we are prerolled we
want to report the position of the segment start value.

When we go into emergency rendering, post a warning informing the user about
this fact.

Fix stepping and position reporting in reverse playback.

Use the start_time of the element as the point from where the step operation
starts. This fixes stepping in all paused states.

When a subclass is blocking in _wait_preroll() in the _render method, make sure
we can unlock the subclass and detect this return value from the render method.

Update framestep document, we want to pass the flush flag in the step-done
message.

Add flush flag to the gstmessage.

Update examples to use the new step-done message api.

Implement framestep with playback rates < 0.0 too.

Dump the step_done message contents.
Sync against the clock when going to PLAYING.

Pass running_time around so that the stepping code can calculate the elapsed
time correctly.

Make start and stop_stepping methods and move their invocation in the right
places.

Perform the atual stepping operation where we have full context about the
timestamps.

Unlock the prerolled frame and recheck if we need to step.
Keep a simple counter for the frames we're about to skip while stepping and
preroll/post step_done when stepping finished.

Add new STEP event and methods for creating/parsing the event
Update design docs.
Add new STEP_DONE message and method to create/parse.

API: GstEvent::gst_event_new_step()
API: GstEvent::gst_event_parse_step()
API: GstMessage::gst_message_new_step_done()
API: GstMessage::gst_message_parse_step_done()

Fixes minor memory leak in unit tests caused by the recent changes.
Since we're expected to take ownership of the GValue in the structure
field struct here, we need to unset it if we don't use it.

Added another tests to check some worries in Bug #582564.

Out-of-band events might lead to us calling g_object_notify() from a
non-streaming thread, which can cause crashes if g_object_notify() is
being called from the streaming thread at the same time. See #554460.

GObject may crash if two threads do concurrent g_object_notify() on the same
object. This may happen if fakesink receives an out-of-band event such as
FLUSH_START while processing a buffer or serialised event in the streaming
thread. Since this may happen with the default settings during a common
operation like a seek, and there seems to be little chance of a timely fix
in GObject (see #166020), we should hack around this issue by protecting all
of fakesink's direct g_object_notify() calls with a lock.

Also add unit test for the above.

Fixes #554460.

Make gst_tag_list_get_string() return FALSE for NULL strings and
empty strings, and gst_tag_list_get_pointer() return FALSE for
NULL pointers, like we do with dates and buffers.

Fixes #560345.

Also warn if an element or application tries to add a field with an
empty string to a structure (NULL strings are still needed and
allowed though) and do all those checks in the right function.

Fixes #559643.

Add convenience wrapper for gst_structure_id_empty_new() plus
gst_structure_id_set() and use it in a few places.

API: gst_structure_id_new()

Use gst_structure_id_empty_new() in combination with GST_QUARK
rather than gst_structure_id_new() when creating message, event,
query and taglist structures. Mostly just because we can.

Deprecate the old _set_stream_time and _get_last_stream_time methods because
they are now equivalent to the better named _set/_get_start_time.

Use the element START_TIME to keep track of the running time when the pipeline
paused so that it can be used to restore the base_time.
Take the start_time before setting the children to PAUSED so that we can
distribute the start_time to the children.