gst/playback/gstplaybasebin.c: Make http sources send special headers so that we...

gst/playback/gstplaybasebin.c: Make http sources send special headers so that we receive icecast metadata if the http...

Original commit message from CVS:
* gst/playback/gstplaybasebin.c: (gen_source_element):
Make http sources send special headers so that we receive
icecast metadata if the http stream is an icecast stream
(otherwise the server will just ignore them). This also
means that from now on users will need the 'icydemux'
element from gst-plugins-good installed if they want to
listen to icecast radio streams. (#341432, #333657).