gst/rtp/: Added preliminary ASF depayloader.

gst/rtp/: Added preliminary ASF depayloader.

Original commit message from CVS:
* gst/rtp/gstrtp.c: (plugin_init):
* gst/rtp/gstrtpasfdepay.c: (gst_rtp_asf_depay_base_init),
(gst_rtp_asf_depay_class_init), (gst_rtp_asf_depay_init),
(decode_base64), (gst_rtp_asf_depay_setcaps),
(gst_rtp_asf_depay_process), (gst_rtp_asf_depay_set_property),
(gst_rtp_asf_depay_get_property), (gst_rtp_asf_depay_change_state),
(gst_rtp_asf_depay_plugin_init):
* gst/rtp/gstrtpasfdepay.h:
Added preliminary ASF depayloader.
* gst/rtp/gstrtph264depay.c: (decode_base64):
Fix base64 decoding.