gst/rtp/gstrtph264depay.*: Add experimental support for outputting quicktime-like AVC output in addition to the exist...

Original commit message from CVS:
* gst/rtp/gstrtph264depay.c: (gst_rtp_h264_depay_class_init),
(gst_rtp_h264_depay_init), (gst_rtp_h264_depay_set_property),
(gst_rtp_h264_depay_get_property), (gst_rtp_h264_depay_setcaps),
(gst_rtp_h264_depay_process):
* gst/rtp/gstrtph264depay.h:
Add experimental support for outputting quicktime-like AVC output in
addition to the existing bytestream output.
* gst/rtp/gstrtph264pay.c: (gst_h264_scan_mode_get_type),
(gst_rtp_h264_pay_class_init), (gst_rtp_h264_pay_init),
(gst_rtp_h264_pay_setcaps), (gst_rtp_h264_pay_payload_nal),
(gst_rtp_h264_pay_handle_buffer), (gst_rtp_h264_pay_set_property),
(gst_rtp_h264_pay_get_property):
* gst/rtp/gstrtph264pay.h:
Make the parsing mode configurable, for some inputs we don't need to
scan every byte for start codes.
Only set the marker bit on ACCESS units.