Added HTTP source based on libsoup. Fixes #497020.

Added HTTP source based on libsoup. Fixes #497020.

Original commit message from CVS:
Patch by: Wouter Cloetens <wouter at mind dot be>
* configure.ac:
* ext/Makefile.am:
* ext/soup/Makefile.am:
* ext/soup/gstsouphttpsrc.c: (_do_init),
(gst_souphttp_src_base_init), (gst_souphttp_src_class_init),
(gst_souphttp_src_init), (gst_souphttp_src_dispose),
(gst_souphttp_src_set_property), (gst_souphttp_src_get_property),
(gst_souphttp_src_create), (gst_souphttp_src_start),
(gst_souphttp_src_stop), (gst_souphttp_src_unlock),
(gst_souphttp_src_set_location), (soup_got_chunk), (soup_response),
(soup_session_close), (plugin_init):
* ext/soup/gstsouphttpsrc.h:
Added HTTP source based on libsoup. Fixes #497020.