examples/gstplay/Makefile.am: Adding the interface library.

examples/gstplay/Makefile.am: Adding the interface library.

Original commit message from CVS:
* examples/gstplay/Makefile.am: Adding the interface library.
* gst-libs/gst/play/Makefile.am: Adding the interface library.
* gst-libs/gst/play/gstplay.c: (gst_play_set_video_sink): Connecting tothe XOverlay size signal instead of GstVideoSink.
* gst-libs/gst/play/gstplay.h: Including the XOverlay interface to check        GST_IS_X_OVERLAY before signal connect.
* gst-libs/gst/video/gstvideosink.c: (gst_videosink_class_init):
Removing the have_video_size signal.
* gst-libs/gst/video/gstvideosink.h: Removing the have_video_size signal        and associated public method.
* sys/ximage/ximagesink.c: (gst_ximagesink_handle_xevents),
(gst_ximagesink_sinkconnect): Using XOverlay public method to fire size
signal.
* sys/xvideo/xvideosink.c: (gst_xvideosink_sinkconnect),
(gst_xvideosink_xwindow_new): Using XOverlay public method to fire size
signal.
* sys/xvimage/xvimagesink.c: (gst_xvimagesink_sinkconnect):
Using XOverlay public method to fire size signal.