h264parse: set a preroll flag when config nals are received through sinkpad
h264parse: flush the last nal in the GstAdapter when a EOS event is caught

When an H.264 bytestream is sent by a previous plugin, a last nal
packet remains in the GstAdapter and is cleared after playback ends.
h264parse looks at a next nal startcode in order to detect nal boundaries,
and so it can't find the end of the last nal.
This change pushes a nal start code to the adapter when an EOS event is caught.

This patch is released by Pioneer.
dfb-video-example: remove duplicate test to determine if audio decoder was sucessfully created.

The test doesn't need to be duplicated in each branch of the 'if' statement.
Once, after the 'if' is cleaner.
dfb-video-example: fix incorrect log messages
dfb-example/dfb-video-example: fix some lacks of object's refcount being decreased
ext/dfbvideosink: add new properties to specify color to fill a surface

The value of each of red, green, blue and alpha can be specified
using these properties. The specified color will be used to fill
a surface when it is cleared.
dfb-example/dfb-video-example: remove clearing a surface before the pipeline running

It is not necessary because a external surface will be cleared
at the initialization of dfbvideosink.
ext/dfbvideosink: add a new property to specify the layer cooperative level

This property can specify the layer cooperative level, which can be
selected by setting the string, "administrative" or "exclusive".
When the cursor is required, "administrative" should be set.
ext/dfbvideosink: don't use the cursor in the exclusive mode

When using the exclusive mode, EnableCusor() wouldn't be available
in the DirectFB 1.6.0 and later.
This patch determines to invoke EnableCusor() if the layer mode is
the administrative.
dfb-video-example: fix a memory leaks caused by illegal usage of gst_pad_get_name()

A gchar pointer passed by gst_pad_get_name() should be free.
This patch adds appropriate g_free() to dfb-video-example and
video-ctrl-example to free the memory.